A QUIZ MANUAL 
OF 
HISTOLOGY, 
General and Dental, 
BY 
CHARLES B. REED, M: D., 
PROFESSOR OF GENERAL HISTOLOGY NORTHWESTERN UNIVERSITY DENTAL 
SCHOOL; ASSISTANT OBSTETRICIAN CHICAGO LYING-IN HOSPITAL; 
DEMONSTRATOR OF OBSTETRICS CHICAGO MEDICAL 
COLLEGE, ETC., 
AND 
FREDERICK B. NOYES, B. A., D. D. S. 
PROFESSOR OF DENTAL HISTOLOGY NORTHWESTERN UNIVERSITY 
DENTAL SCHOOL. 
THE W. T. KEENER CO., 
CHICAGO: 
189 7. COPYRIGHT, 
1897, 
The W. T. Keener Co. CONTENTS. 
GENERAL HISTOLOGY I 
Connective Tissue 13 
Cartilage 15 
Bone 17 
Muscle 24 
Nervous Tissues 28 
Nerve Fibres 31 
Peripheral Nerve Endings 34 
Termination of Sensory Nerves. 34 
Nerve Endings in Smooth Muscle 38 
Striated Muscle 38 
Tendons 39 
Blood Vessels 40 
Glands 40 
Perceptive Apparatus 41 
The Circulatory System 41 
The Heart 42 
The Arteries 44 
The Veins 46 
The Capillaries 47 
The Blood 48 
The Red Cell ;. 49 
Development of Blood Corpuscles So 
The Lymphatic System 51 
Lymphatic Tissues 52 
The Spleen 55 
The Thymus Body 56 
Mucous Membranes 57 
Papillae and Villi i.... 58 
Glands and Mucous Membranes 58 
The Thyroid Body 61 
Salivary Glands 62 IV 
CONTENTS. 
DIGESTIVE TRACT 
The Tongue 69 
Tonsils 73 
Pharynx 73 
Oesophagus 75 
Stomach 77 
Intestines 81 
The Liver 85 
The Pancreas 88 
THE URINARY ORGANS. 
The Kidney 91 
Ureters 97 
The Bladder ' 97 
The Urethra 98 
MALE REPRODUCTIVE ORGANS. 
Penis 101 
Testicle 102 
Semen 106 
The Prostate Body 106 
FEMALE REPRODUCTIVE ORGANS. 
Ovary 109 
Parovarium 112 
Fallopian Tube ..113 
The Uterus 114 
RESPIRATORY SYSTEM. 
Vagina and Genitals 118 
The Larynx 121 
The Trachea 123 
The Bronchi 125 
The Lungs 127 
The Pleura 129 
SKIN AND APPENDAGES 131 
The Hair 135 
Glands of the Skin 138 
Central Nervous System 141 
The Brain 148 
Cerebrum 148 
Cerebral Ganglia ~..,,,.....,,,..,.,,.,,..151 CONTENTS. 
Gray Substance of Ventricles 151 
Cerebellum 151 
The Membranes 154 
Supra Renal Body 156 
DENTAL HISTOLOGY. 
Dental Tissues 159 
Enamel xgx 
Dentine 167 
CeMENTUM 173 
Pulp 177 
Peridental Membrane 183 
Embryology 195 PREFACE. 
An experience of some years in teaching Histology has led the 
writers to believe that a clear conception of the work by the young 
student is a matter of considerable difficulty, and that such a Manual 
as the present would be of value in giving him a better foundation 
for his subsequent study. 
If this object can be attained the purpose of the book will be ac- 
complished. 
No claim for originality is made, either in the design or in the 
subject matter of the work except in the chapter on Denial Histology, 
which it is believed presents to the student for the first time a con- 
cise resume of all the recent available literature. 
To avoid the rather cumbersome words “crown-wards” and “apex- 
wards,” the words up and down, above and below, have been used 
with reference to the crown and the apex of the root and not to the 
position in the jaw; “up” meaning toward the apex; “down” meaning 
toward the crown; “above” meaning nearer the apex; “below,” nearer 
the crown. 
It is desired herewith to acknowledge obligations to the works of 
Piersol, Stohr, Schaefer and Stirling, as well as to many periodicals 
whose pages were freely consulted in the preparation of the work. 
In addition it is desired to acknowledge the obligations due to Dr. 
V. G. Black, of the Northwestern Union Dental School, and to Drs. 
Weller Van Hook and F. X. Walls of the Medical Department of the 
University, for their kindness in reviewing the manuscript. GENERAL HISTOLOGY. 
What is animal Histology ? 
Animal Histology is the science which treats of the 
structural elements of the animal organism and their 
relations. 
What are structural elements ? 
Cells or their products. 
What is a cell ? 
A structural element which under suitable conditions 
is able to nourish itself, develop and reproduce. 
What is a fibre? 
An elongated, modified cell. 
From what is the animal body developed ? 
From a single cell—the impregnated ovum—by re- 
peated division. 
When are cells alike in form ? 
In the embryonic state, before their development 
has begun, they are spherical and indistinguishable 
from each other. 
What is meant by differentiation of cells ? 
As cells develop they change to accord with their 
future destiny, and this is called differentiation. 
What is an elementary tissue ? 
A combination of similarly differentiated cells and 
their products. 2 
GENERAL HISTOLOGY. 
Name the elemental tissues. 
Epithelial, connective, muscular and nervous. 
What is intercellular substance ? 
The product of cell action which is deposited be- 
tween the cells. 
What are the vegetative tissues? 
The epithelial and connective tissues are called veg- 
etative because they occur usually in vegetable as well 
as in animal organisms. 
What are the essential parts of a cell ? 
The protoplasm and nucleus. 
What is the protoplasm ? 
A soft, highly distensible semi-fluid substance which 
constitutes the major portion of the cell. 
What are its chemical characteristics ? 
It is composed principally of albuminoid substances, 
but also contains much water and salts insoluble in 
water; it is alkaline in reaction, and contains a special 
nitrogenous proteid plastin. 
What is the structure of protoplasm ? 
A reticulum (spongioplasm) which is embedded in 
an amorphous ground substance called the hyaloplasm. 
What is the cell wall? 
A membrane surrounding the cell; usually a special- 
ization of the protoplasm or a transformation of the 
peripheral zone of the cell. It is not always present. 
What is the nucleus ? 
A minute vesicular body, generally found near the 
center of the cell. GENERAL HISTOLOGY. 
3 
What is its form ? 
Generally round or oval, but it may be irregular in 
shape. 
Qf what is the nucleus composed ? 
Five proteids, which are usually grouped as chro- 
matin and achromatin. 
Chromatin or nuclein, ) , 
Pyrenin or para nuclein, j c roma in> 
Linin. 
Nuclear fluid or matrix, ) , , • 
A ’ y achromatm. 
Amphipynn, ) 
Why are they so named ? 
The elements called chromatin (Greek chroma, col- 
or), are so called because they are easily stained with 
certain reagents, and achromatin because they are 
stained with difficulty. 
What is the centrosome ? 
A minute corpuscle found near the nucleus from 
which fine threads extend to the chromatin cords and 
to the nuclear membrane. 
How many nuclei do cells possess ? 
A cell usually has but one nucleus, but sometimes 
several nuclei are present, Non-nucleated cells, such 
as red blood corpuscles, originally possessed nuclei, 
but lost them in development. 
What is the nuclear membrane ? 
The structureless membrane which surrounds the 
nucleus and corresponds to the cell wall. 
What is the function of the nucleus ? 
The presence of the nucleus appears to be essential 
to the growth and nutrition of the protoplasm, but 4 
GENERAL HISTOLOGY. 
undoubtedly its most important function is connected 
with the reproduction of the cell. 
What is the nucleolus ? 
A small, highly refracting body found within the 
nucleus and probably of different chemical composi- 
tion; its true value is not yet determined. 
What is the form of a cell ? 
It may possess any shape, depending on the pres- 
ence or absence of pressure and the kind of pressure 
when applied. They may be spherical, like embry- 
onic cells, discoid, polyhedral, columnar, cylindrical, 
cubical, spindle-shaped, stellate, etc. 
How large is a cell ? 
Cells differ greatly in size and are found to vary 
from 1-6000 in. in diameter up to an ostrich egg. The 
human red blood corpuscle measures about 1-3200 in., 
or from to 8/x in diameter. 
What are the vital manifestations of cells ? 
The characteristics which distinguish living from 
inorganic units are: 
S metabolism, 
growth, 
reproduction, 
Animal, I ‘rritabiliiy, 
’ ) motion. 
What is metabolism ? 
The process whereby the cell assimilates those sub- 
stances necessary for its nutrition and function. 
How do cells grow ? 
As a result of metabolism, and equal growth may 
take place in all parts of the cell, but usually unequal GENERAL HISTOLOGY. 
5 
growth takes place and the original form of the cell 
is altered and it becomes flattened, branched, elon- 
gated, etc. 
What is the process of reproduction ? 
Reproduction occurs by direct division—without 
karyokinesis—and by indirect division—with karyo- 
kinesis. 
Describe direct or amitotic division. 
In this process the nuclei of cells rich in protoplasm 
simply divide by constriction without definite grouping 
of nuclear substances; this is a rare and unimportant 
mode of multiplication. 
What is mitotic division ? 
The process whereby the cellular division is pre- 
ceded by certain changes in the nucleus. 
Describe mitotic division. 
Nucleus becomes larger, chromatin increases, fibrils 
contorted—close skein or spirem. 
Chromatin fibrils further thicken, become less con- 
voluted and form irregularly arranged loops—loose 
skein. 
Fibrils separate at their peripheral turns and form 
loops, the closed ends of which are directed toward a 
common, clear center—the polar field. 
Nuclear membrane disappears, achromatin elements 
form nuclear spindle with apices toward poles of the 
future nuclei and the equator occupying polar field, 
at right angles to the chromatin fibres—mother star, 
or aster. 
The loops undergo longitudinal cleavage, splitting 
up into double the number of segments—cleavage. 
Segments separate into two equal groups and pass 6 
GENERAL HISTOLOGY. 
along the guiding lines' of the spindle in opposite 
directions to the poles. The chromatin segments be- 
come crowded about the equator of the spindle during 
migration and form a compressed mass—equatorial 
plate. 
Fibrils are grouped about the poles of the spindle 
and form two rosettes—daughter stars. 
Cell protoplasm begins to divide and continues until 
separated into two bodies enveloping the new nuclei. 
Changes now appear as at first, but in inverse order; 
loose skein, close skein, completion of new nuclei, ap- 
pearance of nuclear membranes, appearance of nucleoli. 
Daughter skeins. 
What is the duration of cell division ? 
From one-half hour in man to five hours in am 
phibians. 
Define irritability. 
Irritability is the property of living matter whereby 
external influences are responded to by changes within 
the cell. 
Describe the phenomena of motion. 
Motion occurs more particularly in the form of cili- 
ary motion in cells and in the contraction of fibres 
in muscles. Amoeboid activity has been observed in 
nearly all the cells of the animal body, and especially 
in leucocytes. 
EPITHELIAL TISSUES. 
Why is this tissue so named ? 
Because it is composed of epithelial cells and a 
relatively small amount of inter-cellular substance. GENERAL HISTOLOGY. 
7 
What is the shape of epithelial cells ? 
Being soft and plastic, and yielding readily to pres- 
sure, the shape of the cells depends upon the amount 
and the kind of pressure to which they are subjected. 
How are the cells nourished ? 
Having no blood vessels, the nutrition of the tissue 
is maintained by absorption of the nutritive juices 
from the intercellular substance. 
What of the nerve supply ? 
Nerve supply is usually scanty but in certain re- 
gions, as the cornea and the fingers, high sensibility 
is found and the presence of nerve terminations among 
the epithelial elements is definitely established. 
How Is the epithelium regenerated ? 
karyokinesis. 
What is the membrana propria ? 
A modification of fibrous tissue, a basement mem- 
brane upon which epithelial cells usually rest. 
What are the principal divisions of epithelium ? 
Squamous, I simple: one layer 
’ ( stratified: several layers. 
Col-nar, | 
i ciliated, 
goblet, 
pigmented. 
Specialized, \ glandular 
( neuro-epithelium. 
Where are they found, respectively? 
Piersol gives distribution as follows: 
Simple squamous epithelium occurs in but few pla- 
ces; 8 
GENERAL HISTOLOGY. 
Partially lining the tympanic cavity, including the 
mastoid cells; parts of the membranous labyrinth; 
the infundibula and alveoli of the lungs; the posterior 
surface of the anterior capsule of the crystalline lens; 
parts of the ducts of glands; the capsule of the Mal- 
pighian body and the descending limb of Henle’s loop 
in the kidney; choroid plexuses and parts of brain- 
ventricles. 
Stratified squamous epithelium occurs widely dis- 
tributed, covering— 
The skin and its extensions, as the external auditory 
canal, conjunctival sac, and cornea; the mouth, lower 
part of pharynx, and oesophagus; the epiglottis and 
upper part of larynx, together with the false and true 
vocal cords; the pelvis of kidney, ureter, bladder, be- 
ginning and end of male and entire female urethra. 
Simple columnar epithelium occurs: 
a. Non-ciliated, in— 
The digestive tract, from the oesophageal opening 
of the stomach to anus, as well as in the larger ducts 
of the glands communicating with this tube; ducts of 
mammary glands; seminal vesicles and ejaculatory 
ducts; membranous and penile portions of urethra. 
b. Ciliated, in— 
Oviduct, uterus, and part of canal of cervix; greater 
part of brain-ventricles and canal of spinal cord. 
Stratified columnar epithelium occurs: 
a. Non-ciliated, in 
Terminal part of the vas deferens; olfactory part of 
nasal fossae. 
b. Ciliated, in— 
The Eustachian tube and parts of tympanic cavity; 
lachrymal passages; respiratory part of nasal fossae, 
with communicating sinuses; ventricle of larynx, tra- GENERAL HISTOLOGY. 
9 
chea, and bronchii; epididymis and first part of vas 
deferens. 
In general, where is stratified epithelium found ? 
Upon every part of the body where constant friction 
results in rapid desquamation of the cells. 
In general, where are ciliae found ? 
Upon all surfaces or canals where motion is required 
to propel the products of gland activity toward an out- 
let. 
Describe simple squamous epithelium. 
It occurs as a simple layer of flattened, polyhedral, 
nucleated plates, and is rare in the human body—outer 
layer of retina, etc., and a few other places. 
Describe stratified squamous epithelium. 
An arrangement of several superimposed layers of 
cells, differing materially from each other in form, size, 
and appearance, according to the layer from which 
they are taken. 
What is the appearance of cells taken from the 
deepest layer? 
They are irregularly columnar, and being young, 
would be spherical if not compressed. They rest on 
the membrana propria and so irregularly that clefts are 
left, whereby nutrient juices and leucocytes can ap- 
proach the cells. 
What of the next layer ? 
They are irregularly polyhedral and are sometimes 
mutually connected by means of delicate processes 
which establish direct continuity between the cells. 
What are prickle cells ? 
The cells of the middle layer which, when dissociated, 10 
GENERAL HISTOLOGY. 
appear to possess spines where the processes were, and 
for this reason are named prickle cells. 
Describe the ceils of the upper surface. 
As the cells approach the surface they become flat- 
tened and keratose and are finally cast off as dead 
scales. 
What is the shape of columnar cells ? 
Seen from the side, they present an elongated 
appearance, the height considerably exceeding the 
breadth; and seen from above, they are hexagonal—in 
reality, therefore, they are prismatic. 
Where is simple columnar epithelium found ? 
Throughout the intestine. 
Mow are columnar cells disposed? 
They rest in a single layer upon the membrana pro- 
pria and their sides are joined with relative accuracy. 
What is the marginal zone ? 
A peculiar appearance found on the free borders of 
columnar cells in some localities, which exhibits a nar- 
row vertical striation and on the addition of water 
breaks up into a series of rods. The striae are prolon- 
gations of processes of the protoplasm that penetrate 
the homogeneous zone. 
Where is stratified columnar epithelium found ? 
This form is found only on the palpebral conjunc- 
tiva and in the main excretory ducts of some of the 
glands and a portion of the male urethra. 
What is its appearance ? 
The outermost cells alone are distinctly columnar, 
the deeper layers spindle shaped, and the deepest 
mainly spherical. GENERAL HISTOLOGY. 
11 
What are ciliae ? 
Specializations of the protoplasm of columnar cells 
m certain localities which appear as minute hair-like 
processes. 
What is their function ? 
By active and constant vibration they create a cur- 
rent which serves to propel mucous and other, bodies 
along the membrane in the direction of the point of 
excretion. 
vVhat are goblet cells ? 
Certain columnar cells distinguished by clear proto- 
plasm and exceptional size whose peculiar elliptical 
shape results from the accumulation of mucous elabo- 
rated within their protoplasm. 
Where are they found ? 
On all surfaces covered by columnar epithelium; es- 
pecially the intestine. 
How do they act ? 
When the distension becomes too great, the cells 
burst in the direction of least resistance and the surface 
°f the membrane is bathed with the secretion. 
What is pigmented epithelium ? 
Cells whose protoplasm has been invaded by melanin, 
whereby the cell acquires a black or brown tint as 
found in the skin of certain races and in the retina of 
the eye. 
What is glandular epithelium ? 
Elements which are permanently modified to engage 
in the elaboration of secretion. 
What is the appearance of glandular epithelium? 
Varying in form from spherical to columnar and 12 
GENERAL HISTOLOGY. 
polyhedral. Such cells are found more or less filled 
with particles of secretion. 
Describe rod epithelium. 
A peculiar striation found in certain cells—i. e., ducts 
of salivary glands—and corresponding to the marginal 
zone. They are found only in secretory cells and have 
some relation to secretory activity. 
What is neuro=epithelium ? 
The perceptive elements produced by high speciali- 
zation of the epithelium of those areas toward which 
the terminations of the nerves of special sense are di- 
rected. 
Describe the cell. 
Two parts are present—an inner containing the nu- 
cleus and corresponding to the protoplasm of the cell, 
and an outer peripherally directed segment which 
sometimes terminates in stiff hair-like processes. 
How does the cel! functionate? 
The outer segment receives the stimuli from external 
impressions, while the inner, centrally directed segment 
stands in close anatomical relation to the nerve fibres. 
What is endothelium ? 
An aggregation of cells of the endothelial type 
which covers the free surface of those spaces not di- 
rectly connecting with the air, such as the serous cavi- 
ties. 
Describe the endothelial cells. 
These cells occur in a single layer of thin, irregularly 
polyhedral plates joined edge to edge. 
What is the origin of endothelium ? 
Endothelium is a connective tissue structure arising 
from the mesoderm. GENE HAL HISTOLOGY. 
13 
CONNECTIVE TISSUE. 
What is the origin of connective tissue ? 
From the mesoblast. 
How are the various kinds of connective tissue pro= 
duced ? 
By differentiation and specialization of intercellular 
substance. 
Wherein does connective tissue differ conspicuously 
from epithelium ? 
In the great predominance of the intercellular sub- 
stance, in its many differentiations and functional im- 
portance. 
How are connective tissues divided ? 
According to the nature of the intercellular sub- 
stance; as, connective tissue, cartilage, and bone. 
What are the cellular elements of connective tissue ? 
They are two : fixed or connective tissue cells 
proper and migratory or wandering cells. 
Describe the fixed cell. 
The fixed cell in its typical condition is a flattened, 
polygonal or stellate plate, and the protoplasm some- 
times extends in several planes as thin, plate-like 
wings. 
The nucleus occupies the thicker part of the body of 
the cell and processes extend into the protoplasm. It 
is limited by a distinct membrane and frequently con- 
tains a nucleolus. 
What is its history ? 
Owing to its participation in the formation of inter- 
cellular tissue, the expanded cell soon becomes reduced 
to the inconspicuous spindle cell of adult areolar tissue 14 
general histology. 
with only a thin envelope of protoplasm around the 
nucleus. Under favorable conditions it is capable of 
exhibiting amoeboid movements. 
What are the plasma cells of Waldyer? 
Cells of irregular for n consisting of soft protoplasm 
and containing many vacuoles. They are found most 
constantly in young tissues. 
What are pigment cells ? 
Fixed cells with melanin of extra-cellular origin in 
the protoplasm. 
What is the flastzellen or granular cel! ? 
A cell characterized by an affinity for certain anilin 
dyes (dahlia) and the conspicuous granularity of the 
protoplasm. It is supposed to have some relation to 
the formation of adipose tissue. 
What are wandering cells ? 
Small nucleated masses of active protoplasm (leu- 
cocytes) which have passed out of the vessels and 
wander through the surrounding tissue. 
Describe mucous connective tissue. 
This tissue is composed of the fixed cells and a large 
quantity of undifferentiated muciferous, intercellular 
substance together with a few bundles of fine fibrils— 
found only in the umbilical cord in the higher animals. 
Describe areolar tissue. 
It is composed of cells and an abundance of inter- 
cellular substance. The intercellular substance is 
differentiated into fine connective-tissue fibres (o. 
united by cement into bundles of various sizes. The 
bundles are soft, flexible, extensible, characterized by 
longitudinal striation-and a wavy course. GENERAL HISTOLOGY. 
15 
Describe elastic fibres. 
These occur in varying quantities in the matrix of 
areolar tissue. They possess sharp, dark outlines, strong 
refractive power, and a conspicuous resistance to acids 
and alkalies. They usually occur as a network. When 
they predominate in connective-tissue bundles the 
tissue is called elastic tissue; fibrous tissue when fibrous 
bundles predominate. 
What is their origin? 
They arise from a transformation of the matrix. 
What is adipose tissue? 
A tissue composed of connective-tissue cells which 
contain fat globules. 
Describe a “fat cell.” 
Fat globules in connective-tissue cells sometimes 
coalesce and give a spherical form to the cell. This is 
called a “fat cell.” The protoplasm occupies a narrow 
and sometimes almost invisible peripheral zone in some 
part of which lies the flattened nucleus. 
Describe reticular connective tissue. 
It consists of a network of slender bundles of fibrillar 
connective tissue, upon which lie flattened nucleated 
cells, and when the meshes are filled with leucocytes, 
the tissue is known as lymphoid tissue. 
Where is it found? 
It occurs principally in lymph glands and is known 
as adenoid tissue. 
CARTILAGE. 
Describe the matrix. 
The matrix of cartilage is the intercellular sub- 
stance and is dense, easily cut and milk white or yel- 
lowish in color. 16 
GENERAL HISTOLOGY. 
Describe the cells of cartilage. 
Usually spherical or flattened on one side, they lie in 
spaces or lacunae of the matrix, which they fill com- 
pletely. 
What is the perichondrium? 
An envelope of dense connective tissue covering the 
free surface of the cartilage. 
Of what is it composed? 
It is composed of two layers—an outer dense, fibro- 
elastic layer and an inner, much looser stratum. 
How are they named ? 
Fibrous layer and chondro-genetic layer. 
Why is the chondrogenetic layer so named? 
Because it is intimately concerned with the produc- 
tion of new cartilage. 
How are the varieties of cartilage named? 
According as the matrix is free from admixture with 
fibrous tissue or is penetrated by the white fibrous and 
clastic fibres, three varieties are distinguished: 
a. Hyaline cartilage, 
b. Fibro cartilage, 
c. Elastic cartilage. 
Describe hyaline cartilage. 
It is characterized by a faint bluish, pearly, trans- 
parent color and homogeneous matrix. 
How are the cells arranged? 
They occur in groups of two or more, and may or 
may not be separated by a thin hyaline partition. 
How is this explained? 
By the conditions and processes of growth—-they are GENERAL HISTOLOGY. 
the descendants of the original cell which has under- 
gone mitosis, and are thus grouped together. 
Where does hyaline cartilage occur? 
In the respiratory organs, as the costal and articular 
cartilages, synchondroses, etc. 
Describe elastic cartilage. 
This has the same structural peculiarities as hyaline 
cartilage, but is distinguished by the networks of finer 
or coarser elastic fibres that penetrate the matrix, and 
its rather yellowish color. 
How do the elastic fibres arise? 
By a transformation of the matrix, and they appear 
in the vicinity of the cells as minute granules, which 
later are disposed in linear rows and fuse into fibres. 
Where does this tissue occur? 
It occurs as the cartilages of the external ear, of the 
epiglottis of the cartilages of Wrisburg and Santorini, 
and of the vocal processes of the arytenoid cartilages. 
Describe fibro=carti!age. 
The matrix contains an abundance of fibrous con- 
nective tissue in loose bundles extending in all direc- 
tions. 
How do the cells appear? 
The cartilage cells are few in number and have thick 
capsules; they occur in small groups or rows at com- 
paratively wide intervals. 
BONE. 
What is the origin of cartilage? 
From the elements of the mesoderm. 18 
GENERAL HISTOLOGY. 
Where does fibro=cartilage occur? 
As the cartilages of the inter-vertebral discs, the 
public symphysis, the inferior maxillary and sterno- 
clavicular articulations. 
What are the chief characteristics of the osseous 
matrix ? 
This tissue is distinguished by its hardness, solidity, 
and elasticity. 
To what are these properties due? 
They are the result of the intimate blending of 
organic and inorganic substances, and either can be 
removed without destroying the tissues. 
How may this be determined? 
By treatment with acids the inorganic substances are 
removed, the bone is decalcified and rendered flexible 
and easily cut like cartilage. 
Also by cautious heating, theorg inic substances may 
be removed and the bone is calcined. 
What is the composition of the matrix? 
Calcium salts and connective tissue fibrils united by 
a small amount of cement substance in fine or coarse 
bundles so that a compact, or lamellar, and a spongy 
matrix are distinguished. It appears homogeneous or 
faintly striated. 
What are lacunae? 
The numerous spindle-shaped spaces—15-27 long 
found in the matrix. 
What do they contain? 
Nucleated flattened bodies—the “bone cells." GENERAL HISTOLOGY. 
19 
What are canaliculi ? 
Minute branched channels which radiate in all direc- 
tions from the lacunae. 
What is their function? 
They form an inter-communicating system of lymph 
spaces throughout the matrix and carry nutrient fluids 
and contain processes from the bone cells lying in the 
lacunae. 
What are osteoblasts ? 
Cells whose function consists in producing bone. 
How do “bone cells” arise? 
By incorporation of osteoblasts within the matrix. 
What is meant by Haversian canal ? 
Channels from 22/ x to iiO/x. wide, continuous with the 
central marrow cavity and of variable length, contain- 
ing an extension of the bone marrow, and rich in 
blood vessels. 
Of what does this extension consist? 
A delicate connective tissue reticulum, rich in cells, 
blood vessels and lymphatics 
Where do the Haversian canals open? 
On both the outer and inner surfaces. 
What are lamella.'? 
The plates or ribbons into which the bone is divided 
by the lacunae and Haversian canals. 
What is an Haversian system? 
An Haversian canal and its concentrically disposed 
lamellae. 
What are interstitial or ground lamellae? 
The remains of the primary spongy network of peri- 
osteal bone. 20 
GENEBAL HISTOLOGY. 
What are the circumferential or fundamental la= 
me! he ? 
The superficial osseous strata that encircle the bone 
on both its outer and inner free surfaces. 
What is the periosteum ? 
An envelope of vascular connective tissue that 
closely invests the outer surface of all bones except 
the articular facets. 
Of what is it composed? 
Of two layers respectively: the fibrous layer and 
osteogenetic layer. 
What is the appearance of the fibrous layer? 
A covering of dense fibrous connective tissue. 
Describe the osteogenetic layer. 
This is a loose stratum, rich in cells and blood ves- 
sels and contains within its meshes numerous round or 
spindle cells which later become osteoblasts. 
Why is it so named? 
From its intimate connection with the formation of 
bone. 
What are Sharpey’s fibres? 
The transverse or perpendicular fibres that appear 
when the superficial lamellae of decalcified bone are 
forcibly torn off. 
What is their significance? 
They represent periosteal fibres which have failed to 
ossify. 
What is the marrow of bone ? 
Genetically, it is an extension of the osteogenetic 
layer of the periosteum found within the cavities of GENERAL HISTOLOGY. 
21 
bones and extending throughout the osseous tissue, by 
means of nutrient canals. 
What is the color of marrow ? 
When young, it is red, but with age, owing to the 
disposition of fat, it becomes yellow. 
What are the elements of red marrow? 
A delicate connective tissue reticulum supporting a 
rich vascular distribution and the meshes of the tissue 
contain numerous soft connective tissue elements. 
What are osteoclasts? 
Cells especially concerned in the absorption of bone 
and are identical with the giant cells of myeloplaxes. 
(Robin.) 
What is Dentine? 
This tissue is analogous to bone since it is derived 
from embryonal connective tissue, but differs in the 
details of arrangement. Vide teeth, 
What are Volkman’s canals? 
Canals embraced by the circumferential lamellae 
which are not centers of systems like Haversian 
canals. 
What is their function ? 
To carry the perforating vessels. 
What is the ultimate fate of endochondral bone ? 
It is for the most part absorbed. 
What change is first noticed in the production of 
The formation in the cartilage of centers of ossifica- 
tion, consisting of an increase in size of the embryonal 
cartilage cells and of the intercellular substance. 
endochondral bone ? 22 
GENERAL HISTOLOGY. 
What is the second change? 
Rearrangement of the enlarged cells into vertical rows 
around which calcification subsequently occurs. 
What is the next change ? 
The osteogenetic tissue of the periosteum increases 
and sends processes into the solid cartilage toward the 
center of ossification. This is accompanied by the 
absorption of the cartilage until the focus of central 
calcification is reached, and here the primary marrow 
cavity is formed. 
What is the fate of the cartilage cells? 
They undergo degeneration and disappear. 
What is the next process ? 
The periosteal ingrowth—vascularization of the car- 
tilage—continues, the primary marrow cavity is en- 
larged and filled with blood vessels and young cells, 
while the intervening calcified matrix projects into the 
marrow space in irregular processes called trabeculae. 
What is the destiny of the young celts ? 
Some retain their original form and become marrow 
cells or they become fat cells or, most important of all, 
bone-forming cells, osteoblasts, which cover the tra- 
beculae and walls of the marrow cavity in a single layer 
and gradually form bone. 
How is periosteal bone formed? 
By the activity of the osteogenetic layer of the peri- 
osteum. The details of the conversion of osteoblasts 
into bone cells are the same in both cases. 
What is the bone corpuscle? 
The osteoblast, after it is completely surrounded by 
the young matrix, is thus named. GENERAL HISTOLOGY. 
23 
How is spongy converted into compact bone ? 
By the development of additional lamellae within the 
meshes of the primary osseous network. 
What is inter=membranous bone? 
Bone formed from connective tissue instead of carti- 
lage. 
How is this accomplished? 
Isolated bundles of connective tissue calcify, and on 
these osteoblasts derived from embryonal cells arrange 
themselves and produce bone. 
What is endochondral bone? 
Bone formed at the centers of ossification within the 
cartilage. 
What is periosteal bone? 
Bone formed directly from and beneath the perios- 
teum constituting the permanent bones. 
What are Howship’s lacunas? 
Variously sized pits excavated by the osteoclasts and 
within which they lie. 
Recapitulate the phases in development of a tubular, 
long bone ? 
Piersol summarizes as follows: 
1. Solid embryonal cartilage. 
2. Enlargement and rearrangement of cartilage-cells 
and lacunae and calcification of matrix at center of os- 
sification. 
3. Penetration of periosteal tissue to the focus of 
calcification; vascularization of the cartilage. 
4. Formation of medullary spaces by the breaking 
down of lacunae surrounded by the zone of calcifying 
cartilage. 24 
GENERAL HISTOLOGY. 
5. Covering of the surface of calcified cartilage tra- 
beculae by the layer of osteoblasts and the production 
of an enveloping sheath of true bone. 
6, Resulting central network of endochondral bone, 
with gradual absorption of encased cartilage trabeculae. 
7. Absorption of the central spongy bone in shaft 
and formation of central marrow-cavity. 
8. Formation, meanwhile, of peripheral periosteal 
network of spongy bone. 
9. Conversion into compact bone by partial absorp- 
tion of trabeculae to form Haversian spaces; secondary 
deposit of concentric lamellae within these spaces form- 
ing Haversian systems of compact bone. 
10. Absorption of inner lamellae of compact bone 
as the shaft increases in diameter by the deposition be- 
neath the periosteum; production of enlarged medul- 
lary cavity. 
11. Continual absorption of endochondral central 
bone until the latter is found alone in the epiphyses, 
where it continues to be produced at the expense of 
the intermediate cartilage during the entire future 
growth of the bone. 
MUSCLE. 
What is the chief functional characteristic of mus= 
cle ? 
Contractility. 
Wherein does the contractility of muscle cells differ 
from protoplasmic contractility ? 
Protoplasm acts in all directions; muscle along defi- 
nite lines and in limited directions only. 
How is muscle divided for description ? 
Into two classes. GENERAL HISTOLOGY. 
25 
1. Non-striated, smooth or vegetative muscle. 
2. Striated, striped or animal muscle. 
How otherwise ? 
The smooth muscle being generally independent of 
the will is known as involuntary, while the striated 
muscle being subject to volition is called voluntary. 
What are the structural elements ? 
Fibres which are really cells, extraordinarily elon- 
gated. 
Describe the non=striated muscle cell. 
This element consists of a contractile, spindle-shaped 
cylindrical or slightly flattened cell, composed of hom- 
ogeneous protoplasm. 
How large are the cells? 
46 to long and 4to wide. 
What is the sheath? 
A delicate homogeneous structure, resembling elastic 
tissue, which invests the contractile substance of the 
fibre. 
Where is the nucleus ? 
The characteristic, rod-shaped nucleus lies near the 
center of the cell. 
How are the cells disposed ? 
The individual cells are united into bundles or fasci- 
culi, and these into strata or membranes. 
Where does smooth muscle occur? 
In all involuntary organs except the heart. 
Where is the nerve supply obtained ? 
Principally from the sympathetic system. 26 
GENERAL HISTOLOGY. 
Describe striated muscle. 
This form developed from the original embryonic 
cell is composed of long, irregularly cylindrical fibres. 
What are the component parts ? 
1. The sarcolemma. 
2. The nucleus. 
3. Muscle substance. 
What is the sarcolemma? 
A clear, homogeneous elastic sheath or closed sack 
investing each fibre and usually adheres tightly to the 
enclosed muscle substance. 
What is the position of the nucleus ? 
Directly beneath the sarcolemma and usually parallel 
to the long axis of the fibre. 
What is the shape of the nucleus ? 
Oval or fusiform. 
What is the microscopic appearance of the fibre? 
It presents alternately broad, dim and narrower, 
light, transverse striae, owing to different refractive 
properties. 
What is that difference ? 
The dark bands are doubly refractive or anisotropic, 
while the light bands are singly refractive or isotropic. 
Of what are the dark striae composed ? 
Of a series of minute prismatic elements placed side 
by side and separated from one another by a thin layer 
of a substance corresponding to and continuous with 
that forming the light zone. 
How is the Sight zone divided ? 
By a delicate interrupted line or row of dark dots GENEBAL HISTOLOGY. 
27 
known as the intermediate disc or the membrane of 
Krause. 
What is the lateral disc ? 
That part of the light zone, between the intermediate 
disc and the dark bands, are thus named. 
What are ultimate fibrillse? 
Fibres treated with chromic acid fall apart length- 
wise into delicate fibrils, each of which exhibits the 
cross striae. These fibrils are the contractile structural 
elements and are called ultimate fibrillae. 
How are the contractile fibrillae arranged ? 
Grouped into bundles parallel to one another and 
held together bythe sarcoplasm which surrounds them. 
What are the bundles called ? 
Muscle bundles or sarcostyles. 
What are Cohnheim’s areas? 
The dark polygonal areas shown by transverse sec- 
tion of each muscle fibre; it is enclosed by lighter 
lines and under high power exhibits minute punctua- 
tions. 
What is the sarcolemma? 
A structureless sheath representing a cell membrane 
which closely invests each fibre. 
Describe the nucleus. 
This is an oval body placed parallel to the long axis 
of the fibre upon the surface of the muscle substance, 
directly beneath the sarcolemma. 
How are muscles joined to the skeleton? 
By special connective tissue formations, tendons, 
fasciae bursoe and tendon sheaths. 28 
GENERAL HISTOLOGY. 
Of what is a striated muscle composed ? 
Striated muscle fibres disposed lengthwise in parallel 
bundles, and surrounded by a connective tissue sheath 
—the perimysium—which carries the nerves and lymph 
vessels. 
What is the endomysium ? 
The connective tissue sheath surrounding each fibre 
and carrying blood vessels and nerve terminals. 
What is the epimysium ? 
The connective tissue sheath surrounding a number 
of muscle bundles. 
How are tendons composed ? 
They are composed of bundles of fibrous tissue and 
are characterized by the parallel course of the fibres. 
How is the union of muscle with tendons effected? 
By the extension of the endomysium, of the muscle 
fibre and the blending of the tissues. 
What is the structure of fasciae ? 
In part like tendons, but richly provided with elastic 
fibres. 
Describe the tendon sheaths and bursoe. 
Consisting of connective tissue in varying thickness, 
they are lined on the inner side with endothelial cells. 
NERVOUS TISSUES. 
What are the elements of nerve tissue in the em= 
bryonic state? 
Spherical cells called neuroblasts. 
How do they change in development? 
They become elongated and pyriform and the nar- 
row end grows out as a long, delicate process, often a GENERAL HISTOLOGY. 
meter in length, and terminates in a free branched end. 
What is the body of the cell called ? 
A ganglion cell or nerve cell. 
What is the axis cylinder process ? 
The elongated delicate process which grows out of 
the neuroblast. 
What are the collateral fibrils? 
Delicate collateral processes given off from the axis 
cylinder process. 
Where are the dendrites or protoplasmic processes? 
Short processes which arise at other parts of the 
ganglion cell and divide dichotomously. 
What is a neuron ? 
The nerve cell and axis cylinder together constitute 
a neuron. 
What is a neuro=dendron ? 
The presence of a neuron together with dendrites 
and collateral fibrils constitutes a neuro-dendron. 
What is the neurilemma ? 
The outer connective tissue envelope of the axis cyl- 
inder. It is a delicate, structureless membrane against 
the inner side of which lie the oval nuclei surrounded 
by a small amount of protoplasm. 
What is the medullary sheath ? 
The inner connective tissue sheath of the axis cylin- 
der lying just upon the axis cylinder and just below 
the neurilemma. 
How are they disposed ? 
There are stretches where the axis cylinder lies un- 
covered, stretches where it is covered by both the 30 
GENERAL HISTOLOGY. 
neurilemma and medullary sheath, and stretches where 
either alone is found. 
Where are nerve cells found? 
In the ganglia, in the organs of special sense, and 
along the course of cerebro spinal and sympathetic 
nerves, but principally in the central nervous system. 
What of their size and shape? 
Varying in size from to and more, they pre- 
sent spherical, spindle-shaped and irregularly stellate 
forms, the latter caused by the protoplasmic outlines. 
How are the cells named? 
According to the number of processes, as unipolar, 
bipolar, and multipolar. 
What is the composition of ganglion cells? 
They are composed of granular or finely striated 
protoplasm. 
Describe the cell. 
It has a characteristic vesicular nucleus, poor in 
chromatin, and enclosing a conspicuous nucleolus. 
There is no cell membrane, and the protoplasm some- 
times contains yellowish grown pigment granules. 
Describe the axis cylinder. 
Usually single, it is the first outgrowth from the em- 
bryonic spherical cells, and it is characterized by its 
hyaline appearance and smooth outline. Its course is 
cellulifugal--it leads from the cell. 
Describe the protoplasmic processes. 
Usually multiple, they are a later outgrowth of the 
embryonal cell, are thicker, granular or finely striated 
and often varicose. Their course is cellulipetal—toward GENE UAL HISTOLOGY. 
the cell. They undergo repeated dichotomous division 
and terminate in an intricate network of fine fibrils. 
What is a nerve cell of the first type? 
A nerve cell having a long axis cylinder process, 
which becomes the axis cylinder of a medullated nerve 
fibre. 
What is a ganglion cell of the second type? 
A cell possessing only a short axis cylinder which 
divides and subdivides and terminates in the vicinity of 
the cell. 
Describe the “ first=type ” cell. 
The axis cylinder, after giving off a number of fine 
branched twigs—collateral fibrils-—and running an ex- 
tended course as the axis cylinder of a nerve fibre, 
undergoes rapid division and becomes a plexus of deli- 
cate fibrils. 
How do the processes terminate? 
In free endings without anastomosis. 
What is meant by nervous network or nervous 
plexus ? 
The disposition of single nerve fibres to branch off 
from nerve fibre bundles and join other bundles. The 
transition of one nerve fibre into another never occurs. 
NERVE FIBRES. 
How are nerve fibres distinguished ? 
By the presence or absence of the medullary sheath 
into the medullated or white and the non-medullated 
or gray nerve fibres. 
How might they be subdivided further ? 
By the presence or absence of the neurilemma. 32 
GENERAL HISTOLOGY. 
Describe non=medullated fibres without neurilemma. 
They consist of naked axis cylinders, and are found 
in the olfactory nerve, bound together by connective 
tissue. 
What are Remak’s fibres ? 
Fibres of the sympathetic nerve similar to the non- 
medullated fibres; they are transparent, cylindrical and 
grouped in bundles. They are from 3/*. to wide, 
about 2/jl thick and show faint longitudinal striation. 
There are other fibres which may or may not exhibit 
the same structure. 
Describe non=medullated fibres with the neurilemma. 
These consist of axis cylinders enveloped by neuro- 
lemma, and are of the same structure throughout. 
They occur in limited portions of the cerebro spinal 
nerve fibres. 
Describe medullated nerve fibres. 
None of these possess the medullary sheath through- 
out its length. They may be without a neurilemma 
and consist of axis cylinder and medullary sheath. 
Where are these fibres found ? 
Only in the central nervous system. 
Where are medullated fibres with a neurilemma 
found ? 
In the trunk and branches of the cerebro spinal 
nerves, and also in the sympathetic nerve. 
Where does division of the medullated fibres occur ? 
Ist, throughout the central nervous system, princi- 
pally where the collateral fibrils diverge at right angles 
into the white substance. 2nd, in the peripheral ner- 
vous system, shortly before their ultimate distribution. GENERAL HISTOLOGY. 
33 
What is the significance of the axis cylinder? 
It is the essential part of every nerve fibre, and oc- 
casionally has delicate longitudinal striation which in- 
dicates its fibrillar structure. 
What do the fibrillae represent ? 
Each represents a special conducting path and is 
cemented to adjacent fibrillae. 
What is neuroplasm ? 
The finely granular interstitial substance which ce- 
ments fibrillae together. 
Of what is the medullary sheath composed ? 
Of a semi-fluid, highly refracting, fatty substance 
called myelin, which gives the appearance of glistening 
cylinders. 
What are the Schmidt=Lantermann segments? 
Small, conical segments into which the medullary 
sheath is divided by oblique clefts found at irregular 
intervals. 
What are the nodes of Ranvier? 
At regular intervals the medullary substance of the 
fibres is interrupted and the axis cylinder and neuri- 
lemma come in contact. These are called the nodes of 
Ranvier. 
Where does the division of a medullated nerve fibre 
occur ? 
Always at the site of a node of Ranvier. 
What are inter=nodal segments ? 
The parts of the fibre between the nodes are thus 
named. They are usually from 0.08 mm to I mm in 
length. 34 
GENERAL HISTOLOGY. 
What is the neuroglia? 
A peculiar form of connective tissue which secures 
the union of the nervous elements in the central ner- 
vous system. 
How are the elements of nerve tissue united in the 
peripheral nervous system ? 
By connective tissue which contains the blood ves- 
sels. 
PERIPHERAL NERVE ENDINGS. 
TERMINATION OF SENSORY NERVES. 
What changes occur in the sensory nerves in pass= 
ing to ultimate distribution ? 
First the medullary substance is lost at some bifurca- 
tion corresponding to the node of Ranvier; after con- 
tinuing for a variable distance the neurilemma ceases 
and the nuclei become more and more infrequent until 
they finally disappear, and the fibrillae continue as 
naked cylinders (axis) which unite to form a widely 
meshed ground plexus. 
What are the terminal plexuses? 
This is the term applied to the network of primitive 
fibrillae within the connective tissue of the organ sup- 
plied. 
Where are they situated? 
In some cases directly beneath the epithelium and 
represent the ultimate distribution of the fibrillae, but 
in others fibrillae emerge from the plexus, enter the 
epithelium and terminate in pointed or club-shaped 
free endings between the epithelial cells. GENERAL HISTOLOGY. 
35 
How are the most important forms of special sen= 
sory nerve endings grouped ? 
Tactile cells, tactile corpuscles and end bulbs. 
Where are the tactile cells found ? 
In the deeper layers of the epidermis or the adjacent 
stratum of the corium, and may be either simple or 
compound. 
What are simple tactile nerve cells ? 
Oval nucleated elements 5~-i2/x, in size resembling 
ganglion cells. 
What is the tactile meniscus or tactile disc? 
A peculiar crescentic expansion upon which the tac- 
tile cells rest, and with which the nerve is connected. 
What is a compound tactile cell ? 
A combination of two or more simple cells, asso- 
ciated to receive the nerve fibre. 
Where are the tactile discs situated ? 
On the side of the cell which lies nearest to the cen- 
tral nervous system. 
What are the tactile corpuscles of JTeissner? 
Tactile corpuscles of oval shape nearly 1-300 in. long 
by 1-800 in. thick, composed of one, two or more rned- 
ullated nerve fibres which are invested with Henle’s 
sheath—a single connective tissue lamella. 
What changes do the fibres experience before enter= 
ing the corpuscle? 
They undergo numerous windings, and the sheath of 
Henlewith the neurilemma become continuous with 
the fibrous envelope of the corpuscle. 36 
GENERAL HISTOLOGY. 
How are the nerve fibres disposed of ? 
They soon lose their medullary sheath and break 
up into fibrillae which pass in a spiral direction through 
the corpuscle, being connected here and there with ter- 
minal discs. 
How are the tactile cells arranged ? 
They are greatly compressed, and usually of indefi- 
nite outline, the transversely placed nuclei and cell 
walls producing transverse markings. 
Where are the corpuscles of JTeissner found? 
In the skin of all parts of the hand and foot, the 
volar surface of the forearm, the skin of the nipple, in 
the conjunctiva at the edge of lids, skin of lips, and tip 
of tongue. 
Describe the end bulbs. 
These are of cylindrical form and embrace both the 
simple and more highly specialized structures. They 
are described in three parts—the capsule, the inner 
bulb and the nerve fibre. In the simpler forms, the 
body is borne upon a stalk and contains the medullated 
fibre, and possibly a minute blood vessel enveloped in 
connective tissue. 
What is the capsule? 
A prolongation of the sheath of Henle forms a nucle- 
ated capsule. 
What is the inner bulb? 
A cylindrical mass of granular or faintly striated pale 
substance enclosed within the capsule within which the 
free axis cylinder lies, often terminating in a knob-like 
expansion. The medullary substance ends where the 
nerve fibre enters the inner bulb. GENERAL HISTOLOGY. 
37 
What are the corpuscles or Vater or the Pacinian 
bodies ? 
These are elliptical, semi-transparent bodies 2-3 mm 
long and half as broad, which are found along nerves 
supplying the skin of the hands and feet and some 
other places. 
What are the component parts? 
The capsule, the inner bulb and the axis cylinder. 
Describe the capsule. 
It is composed of 25-50 concentric connective tissue 
lamellae, both white and elastic fibres, each of which 
possesses an outer transverse, an inner longitudinal 
layer of fibres and is lined by a single layer of endo- 
thelial cells. 
What occupies the interstices between the lamellae? 
A clear, serous fluid, like lymph, most abundant be 
tween the outer lamellae. 
Describe the inner bulb. 
This occupies the core of the corpuscle and is a light 
granular or faintly striated mass of homogeneous tissue, 
closely resembling protoplasm in which nuclei and 
fibrils are sometimes seen. 
Where is the axis cylinder? 
Within and corresponding to the axis of the inner 
bulb. It ends frequently as a slightly expanded ter- 
minal knob. The medullary substance surrounds the 
axis cylinder as far as the inner bulb and then disap- 
pears. 38 
GENU UAL HISTOLOGY. 
NERVE ENDINGS IN SMOOTH MUSCLE. 
What nerve supplies the non=striated muscle ? 
The sympathetic system sends non-medullated nucle- 
ated fibres, enveloped by a thin perineurium. 
What is the ground plexus ? 
The association of the fibres in small bundles con- 
taining ganglion cells at the nodal points. 
What is the intermediate plexus? 
The small branches given off from the ground plexus 
are thus called. 
Describe the inter=muscular fibrillse? 
These are fine bundles of fibres that extend further 
into the contracting tissue. They pass between the 
muscle cells and probably terminate in pointed or 
slightly thickened free ends. 
STRIATED MUSCLE. 
What systems supply the voluntary muscles? 
Both motor and sensory nerves. 
How are the sensory nerves distributed? 
As loose networks, the fibrillae of which probably 
terminate between the individual muscle fibres. 
Describe the intra=muscular plexus. 
This is composed of the union of medullated fibres 
from the motor system into a network. From this net- 
work small bundles of nerve fibres spring and then di- 
vide so that a single medullated axis cylinder passes 
to each muscle fibre. 
What is the telolemma ? 
At the point where the nerve pierces the sarcolemma GENE UAL HISTOLOGY. 
39 
the medullary substance abruptly ends, while the neu- 
rilemma blended with the sarcolemma forms the peri- 
neuria] sheath, or sheath investing the end organ. This 
sheath is the telolemma. 
Describe the ultimate fibrillae. 
The axis cylinder beneath the muscle sheath con- 
tinues upon the surface of the sarcous substance and 
later breaks up into fibrillae which irregularly unite and 
end in thickened bulbous extremities. 
What is the sole plate ? 
The flattened nucleated mass of soft, faintly granular 
protoplasm in which the nerve terminations are em- 
bedded. It is closely applied to the surface of the 
muscular substance. 
What is the end plate ? 
It is composed of the sole plate together with the 
embedded nerve fibrillae and constitutes the motor disc. 
How many end plates do muscle fibres possess ? 
Usually but one; sometimes, however, there may be 
two or more, and also several nerve fibres may supply 
a single end plate. 
TENDONS. 
Describe *the sensory end plates of tendon. 
These consist of an intricate network of pale non- 
medullated fibres 
What is Qolgi’s corpuscle or tendon spindle ? 
These appear as sharply defined, greatly elongated 
elliptical masses, one end of which extends upon the 
tendon, while the other is usually continuous with the 
adjacent muscle fibres. 40 
GENERAL HISTOLOGY. 
What is the tendon spindle composed of? 
A connective tissue capsule which, embracing two or 
more primary bundles of the tendon, becomes united 
with the sheath of the tendon. The inner surface of 
the spindle is covered with endothelial plates. 
How are the nerve fibres arranged ? 
Two, three or more medullated nerve fibres join the 
organ near its widest part, occasionally at one end. 
After repeated division as medullated fibres, the nerves 
spread out on the surface of the tendon as pale non- 
medullated fibres whose axis cylinders unite to form a 
richly but irregularly meshed figure. In addition to 
the network, the ultimate fibrillae present numerous 
knobbed free ends. 
BLOOD VESSELS. 
What system supplies the blood vessels ? 
The sympathetic. 
How are the fibres disposed? 
In addition to the pale fibres a few non-medullated 
ones assist in the production of the irregular network 
surrounding the larger vessels. From this plexus fine 
branches are given off which ultimately end between 
the muscular bundles of the media and in the fibro- 
elastic tissue of the adventitia. 
How are the capillaries supplied? 
They are accompanied and partly surrounded by 
delicate non-medullated nerve fibres. 
GLANDS. 
What fibres supply the glands? 
Both medullated and non-medullated fibres. GENEBAL HISTOLOGY. 
41 
How are they arranged ? 
In bundles forming an inter-lobular plexus, rich in 
ganglion cells, which accompanies the larger excretory 
ducts and blood vessels. Thin bundles of pale fibres 
can be traced to the primary groups of acini where 
they break up into bundles of free axis cylinders pass- 
ing between the acini. The termination within the 
acini is uncertain. 
PERCEPTIVE APPARATUS. 
How do the nerves of special sense terminate ? 
In highly specialized structures made up of neuro 
epithelium, such as the rod and cone cells of the retina, 
hair cells of internal ear, olfactory and gustatory cells. 
How do these structures act? 
The specialized epithelium receives the external 
stimuli while the nerve fibres provide for their trans- 
mission. No direct anatomical continuity between the 
cells and the fibres can be demonstrated. 
THE CIRCULATORY SYSTEM. 
What tissues compose the blood vessels ? 
Fibrous and elastic connective tissues and smooth 
muscle fibres in varying proportion. 
What is the disposition of the elements ? 
Usually longitudinal in the inner and outer, and cir- 
cular in the middle tunics. 
What exceptions to this are found ? 
In the simple structure of the capillaries, and in the 
complicated structure of the heart. 42 
GENERAL HISTOLOGY. 
THE HEART. 
What three membranes compose the walls of the 
heart ? 
The endocardium, the powerful muscular layer and 
the pericardium. 
Describe the endocardium. 
The endocardium is a connective tissue membrane 
containing smooth muscle fibres and numerous elastic 
fibres. 
Where are the elastic fibres most numerous? 
In the auricles, where they form either a close meshed 
network or are blended into a fenestrated membrane, 
thus giving great elasticity. 
What cells clothe the free surface of the endocar- 
dium ? 
A simple layer of irregularly polyhedral, epithelial 
cells—endothelium. 
What is the arrangement of the muscle fibres? 
The muscle fibres are surrounded by a delicate peri- 
mysium, and united by many lateral processes; the tis- 
sue of the auricles is entirely separate from that of the 
ventricles. 
How are the muscle fibres arranged in the auricles ? 
In the auricles an outer transverse layer, common to 
both, can be distinguished, and in each is found an in- 
dependent longitudinal layer. In addition numerous 
small bundles pursue independent courses in other 
directions. The fibres have no sarcolemma. 
How are the muscle fibres disposed in the ventri- 
cles ? 
The bundles are intricately woven in all directions. GENERAL HISTOLOGY. 
43 
Why? 
So that contraction can take place on all sides. 
What are the annuli fibrosi ? 
Firm tendinous ligaments which lie between the 
auricles and the ventricles from which numerous mus- 
cle fibres have origin. 
Describe the pericardium. 
The pericardium is a connective tissue membrane 
investing the exterior of the heart, and by reflection 
forms the pericardial sac. It is clothed on its outer 
(visceral) and inner (parietal) surface by a single layer 
of endothelium, and has fibrous elastic connective 
tissue beneath. 
How do the layers differ ? 
The parietal pericardium is distinctly thicker than 
the visceral. 
Describe the valves of the heart. 
They are composed of fibrous connective tissue con- 
tinuous with that of the annuli fibrosi, and their sur- 
faces are covered with the endocardium. 
Where are the muscle fibres ? 
They are found only in the roots or attached to the 
edges of the valves. 
How are the blood vessels arranged ? 
In the muscular walls of the heart they form typical 
capillary networks with elongated meshes. 
Describe the lymphatic system. 
The lymph vessels are numerous. They occupy the 
clefts between the muscle fibres and accompany the 
blood vessels. 44 
GENERAL HISTOLOGY. 
Whence is the nerve supply derived ? 
Medullated fibres from the pneumogastric and non- 
medullated fibres from the cervical ganglia. 
THE ARTERIES. 
Name the tunics of the arteries. 
Tunica intima. 
Tunica media. 
Tunica adventitia. 
How are the elements disposed ? 
Longitudinally in the tunica intima and adventitia 
and transversely in the tunica media. 
How are arteries classified ? 
For description into three divisions: small, medium 
and large. 
What is meant by the small arteries? 
The terminal branches just before their transforma- 
tion into capillaries. 
Describe the intima. 
In small arteries it consists of long, spindle-shaped 
epithelial cells and a structureless membrane—the 
internal elastic membrane. 
Describe the media. 
This is composed of a single layer of circularly dis- 
posed unstriped muscle fibres. 
Describe the adventitia. 
Here are found longitudinally disposed bundles of 
connective tissue and elastic fibre. GENERAL HISTOLOGY. 
45 
What is meant by a medium artery? 
All the unmentioned arteries of the body except the 
aorta and pulmonary artery. 
What changes are found in the intima? 
It has increased in thickness owing to the presence 
between the endothelium and internal elastic membrane 
of delicate connective tissue flattened corpuscles and 
elastic fibres. 
Is this subendothelial layer always present? 
It is absent in the cortiac, coeliac, exilliac, renal and 
mesenteric arteries as well as the uterine arteries of 
young individuals. 
What changes are found in the media? 
Wide meshed networks of elastic fibres and several 
layers of muscle fibres are found. 
What is the proportion of the two tissues in the ar- 
teries ? 
Extremely variable—muscle preponderates in the 
coeliae, femoral and radial, and elastic tissue in the car- 
otid, axillary and common illiac. 
What change takes place in the adventitia ? 
It becomes stouter; thick elastic fibres are found at 
the boundary of the media, and many times form a 
continuous layer known as the external elastic mem- 
brane. Occasionally new elements are found, as un- 
striped muscle fibres, but never in continuous layer. 
Describe the endothelium of the large arteries. 
The cells are broader and more polyhedral than in 
medium sized vessels. 
Of what does the sub=epithelial layer consist ? 
Fibrous connective tissue, elastic network and flat- 46 
GENERAL HISTOLOGY. 
tened stellate or spherical cells. The elastic network 
becomes closer meshed as it approaches the intima and 
finally passes into a fenestrated membrane. 
Describe the media. 
This is characterized by a preponderance of elasiic 
tissue, circularly arranged. 
\Vhy does elastic tissue preponderate ? 
The vessel’s proximity to the heart necessitates the 
presence of a tissue that will allow of expansion and 
contraction in unison with the heart pulsations. 
Describe the adventitia. 
It differs from that of medium sized arteries only in 
the absence of the external elastic membrane. 
THE VEINS. 
How many coats have veins ? 
As in the arteries, three coats may be distinguished 
tunica intima, media and adventitia. 
Describe the intima. 
This consists of a single layer of endothelial cells, 
rather broader and more polyhedral than those lining 
arteries. 
How is the subendothelium arranged ? 
In the large veins as distinct lamellae, and contain 
numerous connective tissue corpuscles. 
What structure lies outside the subendothelium ? 
The internal elastic membrane. 
Describe the media. 
Here will be found circular bundles of muscle cells 
and lamellae of fibre elastic tissue in the larger veins. 
In some veins the media has almost no muscle fibre. GENERAL HISTOLOGY. 
47 
What are the component elements of adventitia? 
When well developed it consists of intercrossing 
bundles of connective tissue, elastic fibres and longitu- 
dinal fibres of smooth muscle. 
What are the valves of the veins? 
Folds of the intima, covered on both surfaces by epi- 
thelial cells. 
THE CAPILLARIES 
What are the capillaries ? 
Those minute vessels that establish communication 
between arteries and veins, and provide for the bodily 
nutrition. 
What is the diameter of capillaries? 
They average from to io/*. 
Of what do they consist ? 
A single layer of endothelial cells united by inter- 
cellular cement substance. The true capillary posses- 
ses no muscle cells. 
What are vasa vasorum ? 
Small blood vessels of capillary size that supply 
nutrition to the walls of larger vessels. 
Describe the development of capillaries. 
A minute conical mass appears on the wall of a cap- 
illary; soon this unites with a similar offshoot from a 
neighboring point. Solid at first, they are hollowed 
out by an extension of the lumen of the capillary and 
the walls are differentiated to endothelial cells. 
Whence is the nerve supply for blood vessels de- 
rived ? 
Principally from the sympathetic system. 48 
GENERAL HISTOLOGY. 
What is the peri=vascular lymph space? 
This name is applied to the lymph channels in the 
adventitia which occasionally unite and form a com- 
plete ensheathing sinus. 
What is the carotid gland ? 
A pea-sized flattened ovoid mass lying at the bifur- 
cation of the common carotid artery. 
What is its structure? 
A dense arterial network surrounded by granular 
polyhedral cells, and the whole enveloped in connec- 
tive tissue. 
What is the coccygeal gland ? 
A small body found in front of the apex of the coc- 
cyx in connection with the middle sacral artery. 
What is its structure ? 
It is identical in structure with the carotid gland. 
What is the function of these bodies? 
They are rudimentary, and their nature and function 
is not known. 
THE BLOOD. 
What is the blood? 
A mesodermic tissue possessing a fluid intercellular 
substance—the liquor sanguinis, in which float the 
cellular elements—the blood corpuscles. 
What are the morphological constituents of the 
blood ? 
The white corpuscle, the red corpuscle and the blood 
platelets. 
Where are the white corpuscles found? 
In the blood, lymphatic vessels outside the blood ves- GENERAL HISTOLOGY. 
49 
sels, in bone marrow, adenoid tissue, fibrous connective 
tissue, and also between epithelial and gland cells. 
What are the component parts of the leucocyte or 
white blood corpuscle? 
The leucocyte consists of a protoplasm and nucleus 
and has no cell membrane nor definite form. When 
not engaged in amoeboid activity it is spherical. 
How do they reproduce? 
Either by direct or indirect division. 
How do they compare with red corpuscles? 
They are larger but fewer in number, the proportion 
being about 350 red to one white corpuscle. 
What is their function? 
They exist as a source of reserve active protoplasm for 
the repair of destructive processes in both health and 
disease. They engage in the absorption of solid and 
fatty matters, and a certain part called phagocytes seem 
especially aggressive in their warfare upon foreign sub- 
stances or obnoxious microbes. 
THE RED CELL. 
Give the morphology of red blood corpuscles. 
They are soft, flexible, highly elastic elements and 
possess smooth, slippery surfaces. In man and other 
mammals they have the form of flat, circular discs, 
slightly concave on each surface. 
What is the average diameter ? 
About 1-3200 in. 
What are the constituent parts of the corpuscle? 
The stroma and the hoemaglobin. 50 
GENERAL HISTOLOGY. 
What is the stroma? 
A transparent, colorless, homogeneous and plastic 
substance, extensible and pliable to a high degree. 
What is the hoemaglobin ? 
The hoemaglobin fills the spaces of the stroma and 
imparts to the corpuscle its yellow or yellowish green 
color. It readily decomposes and crystallizes. One 
form of crystallization is hoematin. 
Wherein do the red cells of mammals differ from 
the colored corpuscles of other animals ? 
A nucleus and proper cell membrane are wanting. 
Describe the blood platelets. 
They have a diameter of about % less than the red 
corpuscle and are colorless, round or oval discs, at 
times present in large numbers in the blood. 
What is their function ? 
They seem to possess an active influence in the coag- 
ulation of the blood. 
DEVELOPMENT OF BLOOD CORPUSCLES. 
How do leucocytes originate. 
The lymphatic and adenoid tissues are undoubtedly 
the principal sources of the leucocytes. 
How do colored corpuscles arise? 
From the earliest period of embryonic development, 
and during the whole of life, nucleated colored blood 
cells are found in certain situations. By mitosis they 
give rise to non-nucleated colored blood corpuscles 
which at first contain a nucleus. As centers for the 
formation of the blood in the embryo, the liver and GENERAL HISTOLOGY\ 
51 
later, the spleen, in the adult exclusively, the bone 
marrow may be mentioned. 
THE LYMPHATIC SYSTEM. 
What is comprised in the lymphatic system ? 
The lymphatic tissue, the lymph channels and their 
contents, the lymph. 
What is meant by lymph channels? 
The irregular, interfascicular clefts between the bun- 
dles of fibrous tissue or by vessels with definite walls 
carrying lymph. 
What is comprised in lymphatic tissue? 
The single lymphatic nodule, the compound lymph 
gland and diffuse adenoid tissue. 
What are lymphatic spaces? 
111-defined clefts, universally present, of irregular 
form and size, which are bounded by the neighboring 
bundles of connective tissue and lined by an imperfect 
layer of endothelioid connective tissue cells. 
What is the relation between these spaces and the 
lymphatic vessels ? 
It may be assumed that all interfascicular clefts are 
directly or indirectly connected with the lymphatics. 
What are lymphatic capillaries ? 
Protoplasmic tubes of great delicacy composed of a 
single layer of endothelial plates and formed by the 
union of the lymphatic spaces at the margins of the 
fibrous tissue. 
What is their function ? 
They carry the lymph from the organs to the adja- 
cent lymphatic glands. 52 
GENERAL HISTOLOGY. 
What is the shape of the lymphatic vessels ? 
The contour is irregular and presents numerous dila- 
tations and constrictions that indicate the position of 
imperfect valves consisting of a fold of endothelium, 
often strengthened by a little elastic tissue. 
What are perineurial lymphatic channels ? 
Many nerve trunks are enclosed by lymph channels 
into which lymph spaces of the surrounding tissue 
open. Similar channels enclosing blood vessels are 
called peri-vascular lymph sheaths. 
Describe the walls of large lymphatic vessels. 
In such vessels three coats can be recognized; an in- 
ner or endothelial, middle or muscular, and an outer or 
connective tissue. 
What is the lymph? 
A clear, straw-colored fluid containing cellular ele- 
ments—the lymph corpuscles or leucocytes and gran- 
ules of fat. 
LYMPHATIC TISSUES. 
How does lymphatic tissue usually occur? 
As lymphatic nodules or glands; in some cases, how- 
ever, groups of ill-defined diffuse lymphatic tissue occur, 
as in the pharynx, larynx, etc. 
What does lymphatic tissue comprise? 
Lymphatic, lymphoid or adenoid tissue is composed 
of two elements—the connective tissue reticulum and 
the small round cells contained in the reticulum. 
These cells being identical with the lymph corpuscles 
and leucocytes. GENERAL HISTOLOGY. 
53 
What is the reticulum ? 
Intertwining bundles of connective tissue along the 
fibrous trabeculae of which, and especially at nodal 
points, flattened plate-like or stellate connective tissue 
cells are applied. 
What is diffuse adenoid tissue? 
This is the least specialized form of the lymphoid 
structures and is found in the mucosae of the digestive 
and respiratory tracts. 
Describe the single lymphatic nodules. 
These consist of oval masses of adenoid tissue lim- 
ited by a delicate capsule of fibrous lamellae. They are 
numerous in the respiratory and digestive tracts. 
What are the compound lymphatic follicles? 
These are the lymphatic glands of gross anatomy 
and are formed by the partial fusion of a number of 
simple nodules. 
What is the capsule ? 
A firm envelope enclosing the gland composed of 
fibrous connective tissue, and in the largest glands, some 
bundles of smooth muscle. 
How is the lymph circulation conducted in the 
gland ? 
The afferent vessels conveying the lymph break up at 
the periphery of the nodule into branches which dis- 
tribute the lymph—this in turn is collected and carried 
away. 
What is the hilum ? 
At the point of entrance and exit of the larger blood 
vessels and efferent lymph channels, the capsule dips 
deeply into the gland and forms the hilum. 54 
GENERAL HISTOLOGY. 
How is the tissue within the capsule divided ? 
Into a cortex or peripheral zone and medulla or cen- 
tral portion. 
What are the trabeculae ? 
Bundles of fibrous tissue extending from the inner 
surface of the capsule toward the hilum and dividing 
the cortex into imperfect spherical compartments which 
enclose masses of adenoid tissue called cortical folli- 
cles. 
What is the germinal center? 
A light, rounded area in the cortical follicles where 
karyokinetic figures can always be found. 
What is the function of the cortical follicles ? 
They are centers for the formation of leucocytes 
which pass into the lymph sinuses. 
What are medullary cords? 
The continuation of the trabeculae towards the cen- 
ter of the gland forms a number of elongated compart- 
ments that are thus named. 
What are the lymph sinuses ? 
The spaces included between the trabeculae and the 
dense adenoid tissue. 
Where does the connective tissue reticulum arise? 
From offshoots of the trabeculae. 
How are the blood vessels arranged ? 
In two groups, one of which enters at the periphery 
and supplies the capsule and larger trabeculae, while 
the other enters at the hilum and is principally distri- 
buted to the lymphoid tissue. GENERAL HISTOLOGY. 
55 
THE SPLEEN. 
What structures compose the spleen? 
The capsule and the splenic pulp. 
Describe the capsule. 
The capsule is a dense felt work of fibrous tissue and 
a network of elastic fibres. The outer surface is firmly 
united to the peritoneum except where the peritoneum 
is reflected to stomach and diaphragm and at the 
hilum. 
What are the trabeculae ? 
Numerous cylindrical or band-like prolongations of 
the capsule which penetrate deeply into the interior 
from all sides and form a framework, in the spaces of 
which lies the splenic pulp. 
What tissues comprise the pulp ? 
A delicate connective tissue reticulum and the cellu- 
lar elements. 
What are the cellular elements? 
Partly leucocytes, partly larger nucleated cells, white 
and red blood cells and pigment granules. 
How is the adenoid tissue distributed ? 
As a loose lymphoid tissue with intimately related 
vascular channels, and as spherical masses of dense 
adenoid tissue limited to certain points, and named 
Malpighian corpuscles. 
Where are the JTalpighian corpuscles usually situated? 
In the forks of the smaller arteries, and in such a 
manner that the artery pierces them through the center 
or near the periphery. 56 
GENEBAL HISTOLOGY. 
What is their microscopic appearance? 
In appearance they resemble simple nodules of ade- 
noid tissue. 
What is the history of the Malpighian corpuscle? 
They are temporary structures continually disinte- 
grating and redeveloping. 
How is the arterial blood passed to venous chan= 
nels ? 
Within the pulp the blood probably comes into 
direct contact with the lymphoid tissue and is collected 
by the venous spaces and passed on to the larger veins. 
What is the origin of the lymphatic system ? 
The mesoderm. 
THE THYMUS BODY. 
What is the origin of the thymus body? 
It is epithelial and derived from the endoderm. 
What change takes place as the organ matures? 
There is a rapid invasion of mesodermic tissues until 
the lymphoid type predominates, and the epithelial 
structures becomes mere rudiments. 
Of what does it consist ? 
Usually of two lateral lobes, more or less closely 
united, composed of numbers of globules held together 
by inter-lobular areolar tissue and all enveloped within 
the fibrous capsule of the organ. 
How are the lobules divided ? 
By septa arising from the capsule and penetrating 
the lobes. 
What do the lobules consist of ? 
Adenoid tissue denser at the periphery than in the GENERAL HISTOLOG Y. 
57 
center so that a dark cortical and lighter medullary 
substance can be distinguished. 
What are Hassal’s corpuscles? 
Masses of altered embryonic epithelial cells, concen 
trically striated, found in the medullary substance. 
What is the history of the thymus gland? 
It reaches its highest development about the second 
year, and then undergoes retrogressive changes until 
by the twentieth it has lost its characteristic appearance 
and is replaced by fibrous connective tissue and fat. 
MUCOUS MEMBRANES. 
What is the structure of the mucous membrane? 
Mucous membranes are composed of corium and epi- 
thelium. The epithelium covers the surface, and be- 
neath it lies the corium. 
Describe the epithelium. 
This varies with its location, from squamous and 
stratified, to columnar and ciliated, but it is the most 
constant part of the mucous membrane. Where the 
cells are squamous and stratified, the mucous is derived 
from glands, but where they are columnar or ciliated, a 
large part of the mucous is secreted by the cells. 
What is the corium composed of? 
Connective tissue, either areolar or retiform. 
What lies between the corium and epithelium ? 
Usually the basement membrane. 
What is the JTuscularis Mucosas? 
A delicate zone of involuntary muscle cells, which 
frequently occurs between the corium and the sub- 
mucous tissue. It is a part of the mucous membrane. 58 
GENERAL HISTOLOGY. 
PAPILL/E AND VILLI. 
Describe the papillae. 
These are little processes of the corium of a conical 
form, containing blood vessels and nerves and covered 
with epithelium. They vary in size and serve many 
purposes, of which the chief is probably to minister to 
the senses of taste and touch. 
Describe the villi. 
The villi are best observed in the small intestines. 
They contain blood vessels and lacteals and increase 
the absorbing surface. 
What element is most important in the secretory 
process ? 
GLANDS AND MUCOUS MEMBRANES. 
The nucleated cell. 
How is the cell usually disposed ? 
The cell of polyhedral or columnar form is spread in 
a series over the secreting surface as an epithelium. 
Upon what do the cells rest? 
Generally upon a basement membrane or membrana 
propria, which appears as a delicate homogeneous line 
beneath the epithelium. 
What is the object of the membrana propria? 
It limits and defines the secreting surface and sup- 
ports and connects the secreting cells on one side, 
while the other, in close relation to the blood vessels, 
is bathed in lymph. 
How is the membrana propria formed ? 
Of flattened cells which may be united edge to edge GENERAL HISTOLOGY. 
59 
forming a complete limited membrane, or they may be 
branched and united by their processes. 
How do the cells act ? 
They absorb substances existent in the blood, change 
or convert them into new compounds which they 
excrete. 
How is excretion accomplished ? 
Either by exudation or bursting and destruction of 
the cell. 
What two chief varieties of glands occur ? 
The tubular and saccular, each of which is further 
subdivided into simple and compound. 
Describe the simple tubular glands. 
These usually exist as perfectly straight cylindrical 
depressions, like the peptic glands; more often, how- 
ever, the tubes are somewhat wavy and when very long 
are coiled up like the sweat glands. 
Describe the compound tubular glands. 
These vary from a simple bifurcation of the fundus 
to the intricacy of the tubules of the kindey or testicle. 
Describe the simple saccular glands. 
These do not occur in man, but in the lower types 
they are found as simple enclosures of glandular epi- 
thelium in a somewhat spherical shape. 
Describe the compound saccular or racemose glands. 
These are composed of a multitude of alveoli open- 
ing in clusters into the extremities of a branched tube 
called the duct; they are often filled, rather than lined, 
with secreting cells, 60 
GENERAL HISTOLOGY. 
How are they arranged ? 
They have a distinctly lobular structure, arranged in 
groups around the commencing branches of the duct 
with which their cavities are continuous. 
Differentiate between serous and mucous glands. 
The cells of serous glands are distinctly granular, 
usually spherical, readily stained with carmine, and 
have conspicuous nuclei near the center. 
Mucous glands are distended, very clear and trans- 
parent, slightly stained with carmine, and have the 
nuclei displaced to the outer edge of cells—frequently 
directly beneath the basement membrane. 
Describe the fluid elaborated by serous glands. 
It is thin and watery, appearing within the protoplasm 
of the cells as minute dark granules. 
Differentiate between the serous cells at rest and 
after activity. 
When at rest the cells are loaded with granules and 
appear larger, darker and more granular, while after 
active secretion the cells are exhausted and contain 
fewer granules and appear smaller, clearer and less 
granular. 
What do the mucous glands secrete? 
A clear, viscid, homogeneous substance or mucin, 
with an affinity for hoematoxylin. 
Differentiate between the mucous cell at rest and 
after activity. 
During rest, the cell is loaded with mucoid secretion, 
the nuclei crowded to the periphery, the acinous cells 
appear clear with well-defined outlines and on the 
basement membrane side present a thin zone contain- 
ing the nuclei and granular protoplasm, GENE UAL HISTOLOGY. 
61 
After prolonged secretion the cells contain almost no 
mucous, the protoplasmic threads are more closely 
placed, the cell is smaller, darker and more granular. 
What are the demilunes of fieidenhain ? 
Small crescentic groups of granular, deeply staining 
cells, often seen lying between the clearer elements and 
the basement membrane. They are supposed to be ex- 
hausted cells crowded to the periphery by the younger 
and more active cells, 
What is the origin of glands ? 
The glands develop from a cylindrical ingrowth of 
epithelium into the subjacent mesodermic tissue. 
What is the thyroid body ? 
THE THYROID BODY. 
A compound tubular gland whose excretory canal, 
the thyro-glossal duct, in the early stages of the organ 
connects the tubules with the mucous surface. 
What is the history of the gland ? 
Long before the gland matures the duct is obliter- 
ated, the acini become closed cavities and the organ 
is often classed as a ductless gland. 
Of what does the adult gland consist? 
Of numerous tubular acini united by inter-tubular 
areolar tissue into lobules, which, in turn, are joined 
into lobes by a general external fibrous envelope. 
Describe the acini ? 
They are completely closed and lined with a single 
layer of cuboidal or low columnar epithelium resting 
on a basement membrane. GENERAL HISTOLOGY. 
What is found in the acini ? 
Celloid substance, a viscid yellowish mass produced 
by the cells, detached epithelium, leucocytes, migrated 
plasma cells and sometimes red corpuscles. 
SALIVARY GLANDS. 
How are the accessory digestive glands grouped ? 
Those of the serous type, as the parotid gland and 
pancreas, those of the mucous type, as the sublingual, 
and the mixed or muco-serous, as the sub-maxillary. 
Describe the parotid gland. 
This is a compound sacular or racemose gland envel- 
oped in a fibrous capsule from which septa penetrate 
the organ, dividing it into lobes which in turn are sub- 
divided by fibrous partitions into many lobules, and 
these in turn are composed of ultimate saccules or 
acini. 
Describe Stenson’s duct. 
This is the large excretory duct carried in the inter- 
lobular connective tissue. It is composed of a fibro- 
elastic tunica, propria, lined by a simple low columnar 
epithelium, reinforced externally by fibrous tissue. 
What are the salivary tubes? 
These are the smaller ducts of the glands and the 
cylindrical epithelium becomes taller and shows a ver- 
tical radial striation in its outer zone. 
What are the intermediate tubes ? 
These are the inter-lobular divisions of the ducts 
and the columnar cells are replaced by low, flattened 
cells which finally become continuous with the secret- 
ing cells of the acini. GENERAL HISTOLOGY. 
63 
Describe the acini. 
They are limited by a basement membrane continued 
from the smaller ducts, and are almost completely 
filled with polyhedral, glandular epithelium, the inter- 
cellular clefts representing the beginning of the ducts. 
Describe the sublingual gland. 
This possesses the general arrangement of the paro- 
tid gland, but it possesses no intermediate division of 
the duct—the “mucous” tubes passing directly into the 
acini. The cells of both glands are large and clear 
when quiescent and smaller and more granular after 
functional activity. Demilunes of Heidenhain are 
frequently present. 
Describe the duct of Bartholin. 
This is the excretory duct and is composed mostly of 
fibro-elastic tunica propria lined with a single layer of 
low columnar cells and covered on the outside with a 
supplementary layer of fibrous tissue. 
Describe the submaxillary gland. 
This is a mixed gland and contains lobules of the 
serous type, and adjacent lobules of the mucous type. 
Describe the duct of Wharton. 
This is the excretory duct and resembles Stenson’s 
duct. 
Describe the vascular supply. 
The larger arteries accompany the excretory ducts of 
all the glands into the inter-lobular septa where they 
send off branches between the lobules, and end in rich 
capillary networks enclosing the acini. The veins fol- 
low a similar plan. GEEEBAL HISTOLOGY. 
Describe the disposition of the lymphatics. 
They are represented by inter-fascicular clefts which, 
united with definite lymph vessels, empty into the large 
trunks which accompany blood vessels. 
Describe the nerves of the salivary glands. 
Both medullated and non-medullated fibres are 
found. The nerve fibres can be traced to the basement 
membrane of the acini, but the ultimate distribution is 
not known. 
THE TEETH. 
From the standpoint of comparative anatomy, with 
what structure in lower animals are the teeth an- 
alogous? 
The dermal scales of such animals as the sharks and 
rays. 
Is the tooth a part of the osseous system ? 
No; it is an independent organ held in position in 
the jaw by the alveo-dental periosteum or peridental 
membrane. 
What are the tissues of which the teeth are com= 
posed ? 
(i) Enamel—The hardest structure in the body. 
It covers the exposed part of the tooth, or the crown, 
and gives the characteristic form to it, (2). Dentine 
—Forms the greater portion of the tooth, both root and 
crown. (3) Cementum—or crusta - petrosa covers 
the dentine in the root portion and gives the attach- 
ment to the fibres of the peridental membrane. 
What is the composition of the enamel ? 
Enamel is almost wholly made up of inorganic mat- GENERAL HISTOLOGY. 
65 
ter, containing 95 per cent to 97 per cent inorganic, 3 
per cent to 5 per cent of organic matter. The inor- 
ganic matter is chiefly phosphates of calcium and 
magnesium, carbonates of calcium and magnesium and 
a small amount of flourides. 
Describe the structure of the enamel ? 
The enamel is made up of irregular 4-6 sided prisms, 
the enamel prisms, closely placed and generally verti- 
cal to the surface of the dentine. They are not uniform 
in diameter but present slight varicosities causing the 
alternate light and dark striated appearance in longi- 
tudinal sections. The prisms are held together by a 
slight amount of inter-prismatic or cement-substance 
which is perfectly calcified. The prisms are not 
straight in their course but are more or less wavy, es- 
pecially in the portion forming the cusps. 
What is Nasmeth’s membrane ? 
Nasmeth’s membrane is a delicate but resistant cuti- 
cle composed of keratose epithelial plates, which cover 
the enamel at birth and for a short time after, but is 
soon worn away. 
What is the composition of dentine? 
Dentine is composed of 72 per cent inorganic, 28 
per cent organic matter. Like bone, it is composed of 
an organic matrix into which inorganic salts are de- 
posited, If treated with acids the organic matter is 
left, retaining the form of the tissue. 
What are the dentinal tubules ? 
The dentinal tubules are minute canals which pass 
outward from the pulp cavity to the border of the 
enamel or cementum. They are wavy in their course, 
and in the outer portion of their course branch very 66 
GENERAL HISTOLOGY. 
freely with each other. They are about i.i to 2.5 
microns in diameter. 
What are the inter=globular spaces and where are 
they found? 
The inter-globular spaces are irregular spaces in the 
dentine where the tissue is imperfectly calcified. 
What is the granular layer of Tomes? 
The granular layer of Tomes is the layer of dentine 
just below the enamel or cementum. The appearance 
is caused by the enlarged ends of the dentinal tubules. 
What fill the tubules in life ? 
In life the tubules are filled by processes from the 
odontoblasts. 
What are the odontoblasts? 
The odontoblasts are flask-shaped cells which lie 
next to the dentine on the surface of the pulp. From 
them protoplasmic processes pass outward through the 
dentinal tubules as far as the inner surface of the 
enamel or cementum. The odontoblasts are the cells 
which form the dentine. 
What are the dentinal fibres ? 
The dentinal fibres are the protoplasmic processes 
of the odontoblasts which fill the dentinal tubules. 
What is the difference between cementum and bone ? 
Cementum has no Haversian canals. 
Describe the structure of the cementum. 
Cementum is made up of successive layers resem- 
bling the lamellae of bone. In it are irregular spaces, 
lacunae, like those of bone, which communicate with General histology. 
67 
each other and with the ends of the dentinal tubules by 
the canaliculi. The cementum furnishes attachment 
for the fibres of the peridental membrane. 
What is the dental pulp? 
The dental pulp is the soft tissue filling the cavity 
within the dentine. 
What is the structure of the pulp? 
The pulp is composed of an embryonal connective 
tissue made up of a large amount of gelatinous inter- 
cellular substance in which round, stellate and spindle- 
shaped cells are scattered. The pulp is richly supplied 
with blood. The vessels enter the foramen at the 
apex of the root, pass down and break up into a rich 
plexus in the outer portion. At least one nerve enters 
at the apical foramen and forms a rich plexus of nerves 
just below the layer of odontoblasts. DIGESTIVE TRACT. 
THE TONGUE. 
What composes the bulk of the tongue? 
Variously disposed bundles of striated fibres from 
the lingualis and accessory muscles and over the unat- 
tached surfaces the mucous membrane is reflected. 
How is the muscular tissue arranged ? 
In three planes: 
I. Vertically, and slightly radially (genio-hypo- 
glossus and vertical fibres from lingualis and hypoglos- 
sus). 
2. Transversely (transverse fibres of lingualis.) 
3. Longitudinally (Lingualis superior, inferior and 
styloglossus). 
What is the septum lingualae? 
A vertical median partition dividing the muscular 
tissue into halves. The interfascicular spaces are filled 
by delicate connective tissue, fat and numerous small 
lingual glands. Branched, striated muscle fibres are 
common in the tongue. 
Describe the mucous membrane. 
That on the sides and inferior surfaces is thin and 
contains small papillae and many mucous glands; on 
reaching the upper surface it becomes thcker and pre- 
sents papillae. 
69 70 
GENERAL HISTOLOGY. 
How are the papillae named ? 
With reference to their shape, three kinds are distin- 
guished; the filiform or conical, the fungiform and the 
circumvallate. 
Describe the conical papillae. 
Occurring on all parts of the upper surface of the 
tongue, they consist of a conical or cylindrical eleva- 
tion of the connective tissue of the mucosa, 5-2.5 mm 
in height covered with a thick layer of epithelium, the 
cells of which are partially removed by abrasion be- 
cause of the exposed condition of the papillae. 
Describe the fungiform papillae. 
These are also found on all parts of the tongue, but 
they are fewer, broader and lower than the conical, ap- 
pearing as isolated but distinct red points. The con- 
nective tissue Stalks of these papillae are composed of 
a dense network of fibrous tissue and bear secondary 
papillae on their upper surface, the epithelium com- 
pletely enveloping the connective tissue core. 
Describe the circumvallate papillae. 
Usually eight or ten in number, they are placed in 
two rows forming /\ at the posterior part of the dorsum 
of the tongue. Each consists of a large flattened fungi- 
form papilla surrounded by a deep furrow and a second- 
ary encircling ridge which suggested the name. 
Where are the taste buds? 
These lie within the epithelium, lining the sides of 
the deep circular furrow, and appear as inconspicuous 
oval bodies occupying nearly the whole thickness of 
the epithelium. Others are found in the folds in the 
vicinity of the circumvallate papillae, on some fungiform 
papillae and at the sides of the tongue. DIGESTIVE TRACT. 
71 
What are the papillae foliatae? 
These are parallel folds found just in front of the 
anterior pillars of the fauces and contain a number of 
taste buds. 
Describe the taste buds. 
Each taste bud consists of an enveloping layer of 
greatly elongated epithelial cells called cortical or teg- 
mental cells, and these form a complete covering ex- 
cept at a small point corresponding to the superficial 
pole of the bud, and here a small canal, the taste pore, 
connects the interior of the bud with the surface of the 
mucous membrane. 
What lies within the capsule of the taste bud ? 
A group of highly specialized elements, the gustatory 
cells. 
Describe the gustatory cells. 
They are neuro-epithelial elements, appearing as 
spindle, rod-like or forked cells, possessing an oval 
nucleus near the center. The outer ends of the cells 
are usually prolonged with fine pointed extremities 
and some of them terminate in stiff hair-like processes 
projecting within the taste pore almost to the free 
surface. 
How are the inner ends of the gustatory cells ar= 
ranged ? 
They are prolonged as slender, sometimes forked 
processes showing minute swellings or varicosities. 
What glands are found in the submucous and inter= 
fascicular tissue? 
Mucous and serous glands. 72 
GENERAL HISTOLOGY. 
Where are they situated ? 
The mucous glands are found in the deeper layers of 
the submucous tissue and between the bundles of mus- 
cle fibre in the back part of the tongue. The serous 
glands are limited to the immediate neighborhood of 
the circumvallate and foliate papillae. 
Describe the adenoid tissue of the mucous mem= 
brane. 
This occurs as diffuse masses and as circumscribed 
irregularly spherical lymph follicles I to 5 mm in 
diameter. The position of the follicles is frequently 
indicated by slight elevation of the mucosa in the cen- 
ter of which a minute pit leads to the lymphatic crypt. 
The epithelium lining the crypt is infiltrated with lym- 
phoid cells, while the surrounding diffuse adenoid tis- 
sue contains several minute spherical masses of denser 
structure. 
What are the salivary corpuscles? 
Spherical, nucleated, granular bodies, a little larger 
than leucocytes, derived from the adenoid tissue of the 
mouth. They are really escaped lymphoid cells swol- 
len by fluids. 
Describe the blood supply of the tongue ? 
The vessels form a superficial network in the mucosa 
and send twigs to terminate in the summits of the 
papillae. The acini of the glands and the lymph folli- 
cles are surrounded by capillaries. 
Describe the nerves of the mucous membrane. 
These are derived from the glosso-pharyngeal and 
lingual branch of the fifth, and end either beneath the 
epithelium in the usual manner or in close relation DIGESTIVE TRACT. 
73 
with the organs of special sense—taste buds. Many 
microscopic ganglia occur along their course. 
TONSILS. 
What are the tonsils? 
Compound lymphatic glands, consisting of from ten 
to eighteen lymph follicles embedded in diffuse ade- 
noid tissue. 
What is the capsule ? 
A fibrous structure separating the tonsils from the 
adjacent structures on the attached surface. 
How is it covered on the oral surface ? 
By a reflection of the oral epithelium. 
Describe the epithelium. 
The epithelium covering the folds and depressions is 
completely infiltrated with lymphoid cells so that the 
boundary line between the epithelium and the adjacent 
adenoid tissue is often obscure. 
Describe the mucous glands. 
These are found in the vicinity of the tonsils, into the 
crypts of which they pour their secretion to mingle 
with the shed epithelium and lymphoid cells in the 
recesses. 
Describe the blood vessels and lymphatics. 
These occur in great numbers in the adenoid tissue, 
and also surrounding the organ and receiving radicles 
from the interior. 
PHARYNX. 
What tissues constitute the pharynx ? 
A fibrous tunic on the inside of which lies the mu- 74 
GENERAL HISTOLOGY. 
cous and submucous tissue, and outside are the fibres 
of the constrictor and the muscles. 
What differences distinguish the respiratory from the 
digestive portion of the sac ? 
The variations are mostly in the mucosa and depend 
especially upon the character of the epithelium. 
Describe the epithelium of the upper portion of the 
pharynx. 
The respiratory or upper division of the pharynx is 
clothed with stratified, ciliated, columnar epithelium, 
with numerous goblet cells. 
What epithelium covers the lower portion of the 
tract ? 
Below the level of the soft palate, stratified squamous 
cells are found similar to those lining the oral cavity. 
Describe the tunica propria. 
This is the stroma of the mucosa and is formed of a 
felt work of fibrous tissue and variable qualities of elas- 
tic tissue. 
Where are the papillse? 
The papillse are found where squamous cells cover 
the sub-epithelial surface of the mucosa; they are not 
found beneath ciliated epithelium. 
Where are the pharyngeal glands found ? 
In the deepest layers of the mucosa, especially 
around the orifices of the Eustachian tube. 
How is the adenoid tissue distributed ? 
As lymph follicles existing singly or in groups in the 
upper part of the cavity. DIGESTIVE TRACT. 
75 
What is the pharyngeal tonsil ? 
The aggregation of adenoid tissue found between the 
openings of the Eustachian tubes is so named. 
Describe the submucous tissue. 
This tissue unites the mucous membrane with the 
fibrous coat, whose dense felt work forms a structure 
frequently termed the pharyngeal aponeurosis. Its 
posterior part is thickened and forms the raphe to 
which the constrictor muscles are attached. 
What fibres constitute the muscular coat? 
Striated fibres of the constrictor. 
Where is the areolar tissue? 
This lies external to the muscular coat and attaches 
the pharynx to surrounding structures. 
What structure carries the blood vessels, etc.? 
The blood vessels, lymphatics and nerve trunks are 
supported by the submucosae, and send off branches to 
the mucous membranes of the mouth. 
What nerves supply the pharynx? 
Branches from the cranial and sympathetic trunks 
form the pharyngeal plexus. Both medullated and 
non-medullated fibres are present, associated with 
minute ganglia. 
(ESOPHAGUS. 
What structures comprise the oesophagus ? 
The mucous, submucous, muscular and fibrous coats. 
Describe the mucous coat. 
Stratified, squamous epithelium resting upon the con- 
nective tissue matrix, and the tunica propria, the inner 76 
GENERAL HISTOLOGY. 
surface of which bears numerous papillae. The deeper 
layers of the mucous are separated from the submucous 
coat by longitudinal bundles of involuntary muscle 
called the muscularis mucosas, which first appear a little 
above the middle of the tube. 
Describe the submucous coat. 
This coat is composed of loose connective tissue and 
supports the larger blood vessels and nerves. 
Where are the mucous glands? 
Within the submucosa, and more numerous on the 
anterior surface and especially so at the cardial orifice. 
They are lined for the most part with columnar 
epithelium. 
Describe the muscular coat. 
This consists of two layers, an inner circular and an 
outer longitudinal layer, whose bundles are united by 
connective tissue septa. 
What fibres are found in the oesophagus ? 
In the upper part striated, in the lower part smooth, 
and in the middle both kinds exist, the striated disap- 
pearing as the smooth increases and vice versa. 
Describe the fibrous coat. 
This coat envelopes the muscular coat, externally 
strengthening the tube and affording attachment to the 
surrounding areolar tissue connecting the oesophagus 
with neighboring organs. Considerable elastic tissue 
is found in this coat. 
How are the blood vessels supported ? 
They penetrate the outer coats and ramify in the 
submucous tissue, sending branches to supply the other 
tissues. DIGESTIVE TBACT. 
How are the lymphatics and nerve fibrillas disposed? 
The lymphatics of the deeper layers of the mucosa 
terminate in the submucosa. The nerve fibrillae pass 
from the submucous tunic into the mucosa and termin- 
ate beneath the epithelium. 
STOMACH. 
What coats compose the stomach ? 
The mucous, submucous, muscular and serous or 
fibrous. 
Describe the mucous coat. 
The mucous membrane is covered by a simple 
columnar epithelium, the squamous cells of the oesoph- 
agus abruptly terminating at the cardiac orifice. 
What peculiarities distinguish the gastric mucous 
membrane ? 
The numerous goblet cells which replace the colum- 
nar elements of the epithelium, the conspicuous folds 
or rugae on the inner surface and minute inequalities or 
pits which mark the openings of the gastric glands. 
Describe the gastric glands. 
The gastric glands are of two kinds, the peptic 
glands found in the middle and cardiac thirds, and the 
pyloric glands found in the pyloric third. Both varie- 
ties are limited to the mucosa extending in length the 
entire thickness of this coat. 
How are gastric glands distributed? 
Uniformly through all parts of the stomach in groups 
separated by delicate partitions of connective tissue. 
Describe the peptic glands. 
The peptic glands are slightly wavy, simple tubular GENEBAL HISTOLOGY. 
depressions in which a duct, neck and fundus are 
recognized. 
How is the fundus of the gland disposed ? 
Generally it is tortuous or spiral, but exceptionally it 
is divided and sometimes its extremity is bent at right 
angles to the tube. 
What cells line the glands ? 
Generally columnar epithelium from the mucous 
membrane passes with little change into the ducts, be- 
coming imbricated and toward the neck shorter and 
more spherical in outline. At the neck or narrowest 
part of the tube the cells are more cuboidal and assume 
a columnar form as they approach the fundus. 
What are the chief or central cells ? 
These bound the lumen of the peptic gland and form 
the bulk of the glandular epithelium. Each cell con- 
tains a spherical nucleus embedded within the granular 
protoplasm, the condition of which depends upon the 
state of functional activity. 
What other cells exist in peptic glands? 
The parietal or acid cells are situated in the per- 
iphery of the gland directly beneath the basement 
membrane and separated from the lumen by the inter- 
vening central cells. 
What are intercellular clefts ? 
Minute lateral canals which occur in many places, 
affording direct communication between the parietal 
cells and the lumen of the tube. 
Describe the parietal cells. 
They are irregularly distributed from the fundus to 
the neck of the gland and most numerous in the vicin- DIGESTIVE TRACT. 
79 
ity of the neck. The cells are larger than those in the 
lumen, polygonal in outline, and possess a pale granu- 
lar protoplasm and a round or oval nucleus. 
Describe the pyloric glands? 
These glands possess long, wide ducts into which the 
several divisions of the body open, the tubular subdi- 
visions are wavy and tortuous and the extremities are 
somewhat slightly expanded. The duct is lined by tall 
columnar epithelium which becomes broader toward 
neck and fundus. 
What do the cells contain ? 
A fine granular protoplasm, and do not secrete mu- 
cous but a thin, albuminous fluid. Parietal or acid cells 
do not occur in pyloric glands. 
What are the lenticular glands? 
Patches of diffuse adenoid tissue that lie around and 
among the ends of the gastric follicles near the pylorus. 
Describe the muscularis mucosae. 
This structure is found in the deepest layer of the 
tunica propria and is made up of an inner circular and 
an outer longitudinal layer of non-striped muscle. 
Describe the submucosa. 
This coat is comparatively thick and is composed of 
fibro elastic bundles of variable size, quite loosely in- 
terwoven. The rugae of the stomach involve both 
the mucous and submucous coats, the submucous coat 
forming the connective tissue framework of the eleva- 
tion over which the mucosa lies. The submucosa sup- 
ports the larger blood vessels, lymphatics and nerves. 
Describe the muscular coat. 
This is composed of two sheets of involuntary mus- 80 
GENERAL HISTOLOGY. 
cles arranged as an outer longitudinal and an inner cir- 
cular layer, and near the cardiac end is an imperfect 
oblique layer. 
How is the pyloric orifice arranged ? 
It is guarded by a fold of mucous membrane overly- 
ing the submucosa and reinforced by conspicuous ring- 
like thickenings of the circular layer, forming the 
gastro-duodenal valve. 
Describe the serous coat 
This coat is composed of fibrous connective tissue 
and network of elastic fibres. A simple layer of endo- 
thelial plates covers the peritoneal surface. 
Describe the blood supply of the stomach. 
The large arteries penetrate the outer coat, divide 
within the mucosa and send branches to supply the 
mucous membrane, muscular and serous coats. 
Describe the lymphatics of the stomach. 
The large lymphatics accompany the blood vessels 
and form a plexus in the submucous tissue. A closer 
network in the deeper part of the mucosa sends radi- 
cles up between the glands to the end beneath the epi- 
thelium. The adenoid tissue is drained by peripheral 
lymphatics. 
Describe the nerves of the stomach. 
The nerves occupy a position between the circular 
and longitudinal muscular layers and form a plexus 
containing both pale and medullated fibres. At the 
nodal points ganglia are found and the whole forms 
the plexus of Auerbach. 
What is the plexus of Meissner? 
The intramuscular network continues, and after giv- DIGESTIVE TRACT. 
81 
ing off lateral twigs forms a second ganglionic plexus 
in the submucosa called the plexus of Meissner. 
INTESTINES. 
What coats are found in the intestines? 
The mucous, submucous, muscular and serous. 
Upon what are the variations in the intestine de= 
pendent ? 
Upon modifications and specializations of the mucous 
membrane. 
What are the villi ? 
Small cylindrical elevations projecting into the intes- 
tinal lumen and bathed in the juices of the canal. 
What are the valvulae conniventes ? 
Transverse or oblique folds of the mucosa extend- 
ing partially around the tube, and are most marked in 
the duodenum and jejunum. They serve to increase 
the area of the mucous membrane and are beset with 
villi. 
What cells cover the mucosa? 
A simple layer of columnar epithelium resting on a 
basement membrane. The prismatic cells contain finely 
granular protoplasm. Oval nuclei are situated usually 
within the inner half of the cell. 
Describe the basilar border. 
This is a well-defined, continuous band investing the 
outer free ends of the cells and exhibits a fine vertical 
striation. 
Where are the goblet cells ? 
These are very numerous, but especially so in the 
large intestines. In carmine preparations they appear 82 
GENERAL HISTOLOGY. 
as clear oval breaks in the epithelial outline. Migratory- 
leucocytes are also found in the intercellular clefts. 
What is the endothelium of Debove? 
Flattened connective tissue plates forming a mem- 
brana propria upon which the epithelium rests. 
Describe the villi. 
Derived entirely from the mucosa, the epithelium 
extends over the projecting portion of the tunica pro- 
pria to invest entirely the finger-like processes. 
Where are the lacteals? 
The lacteal occupies the center of each villus and 
ends blindly near the apex of the villus. 
Describe the tissue surrounding the lacteal. 
It consists of a fibrous reticulum holding lymphoid 
cells within its meshes and resembles adenoid tissue. 
Numerous bundles of delicate smooth muscle fibres 
also surround the lacteal and extend from their origin 
in the muscularis mucosae toward the apex of the villus. 
How are the blood vessels distributed ? 
They form a capillary network around the central 
lacteal and extending through the greater part of the 
villus connect the afferent arteriole and efferent veins. 
How are the lacteals affected by digestive activity ? 
When at rest, the lacteals contain lymph, but during 
digestive activity they appear milky on account of the 
emulsion formed by the absorbed oil. 
Where do the villi end ? 
At the ileo-caecal valve, and are not present in the 
small intestine. DIGESTIVE TRACT. 
83 
What glands are found in the intestinal walls? 
The glands of Lieberkuhn and Brunner, and the 
solitary and agminated lymph glands. 
Where are the crypts or glands of Lieberkuhn ? 
They form an almost continuous layer of simple 
tubular depressions throughout the large and small in- 
testines, lying between the bases of the villi in the small 
intestine. 
Describe the crypts of Lieberkuhn. 
They occupy nearly the whole depth of the mucosa, 
and the columnar cells of the free surface pass directly 
into the tubules to become the spherical secreting cells, 
many of them being converted into goblet cells. In 
the large intestines they increase in size, becoming 
longer and possessing wider mouths. 
What are the glands of Brunner? 
They are higher specializations of the pyloric glands 
of the stomach. In passing from the stomach to the 
intestines they undergo repeated division and at the 
same time sink lower and lower into the mucosa, until 
they finally reach a position in the submucosa of the 
duodenum. 
Describe the structure of Brunner’s glands. 
They appear as groups of short, wide, tubular acini, 
disposed about long slender ducts which pass from the 
submucous tissue through the mucosa to open on the 
intestinal surface between the orifices of the follicles in 
the depressions between the bases of the villi. Owing 
to their rapid branching they resemble racemose glands 
rather than the compound tubular glands to which they 
belong. The secretion is serous, not mucous. 84 
GENERAL HISTOLOGY. 
Describe the solitary glands. 
These are isolated lymph follicles scattered through 
the entire intestine. They lie primarily within the 
mucosa but frequently, also, within the submucous coat. 
The adenoid tissue is denser at the periphery than 
toward the center. 
Describe the agminated glands or Peyer’s patches. 
These are large, oval groups of closely associated 
lymph follicles, held together by diffuse adenoid tissue. 
They are usually found in the lower two-thirds of the 
small intestine, and reach their highest development in 
the ileum. They appear first within the mucosa, but 
later encroach largely on the submucosa. 
Describe the muscularis mucosas. 
This occupies the deepest part of the mucosa and 
marks the outer boundary of the mucous layer. It is 
composed of longitudinal fibres and occasionally circu- 
lar fibres of smooth muscle. 
Describe the submucosa. 
This consists of loosely united bundles of fibro elastic 
tissue and supports the large vascular and lymphatic 
trunks. 
Describe the muscular layer. 
This is composed of a relatively thick inner circular 
layer and an outer longitudinal layer separated by a 
thin layer of connective tissue. In the lower part of 
the rectum the circular layer becomes thicker to form 
the internal sphincter. 
Describe the blood vessels of the intestine. 
These follow the general arrangement of those of 
the stomach. Many branches pass from the network 
of the submucosa to be distributed to the deep and su- DIGESTIVE TBACT. 
85 
perficial parts of the mucosa; the tubular glands are 
surrounded by capillary networks, and beneath the 
epithelium wider capillaries encircle the mouths of the 
follicles. These capillaries all connect with venules 
that empty into the large veins of the submucosa. 
For the villi, special branches pass directly to the 
bases, expand into networks which pass around the lac- 
teals as far as the apex and then descend as straight 
veins, receiving in their course the superficial capil- 
laries that encircle the glandular ducts. In Brunner’s 
gland the capillaries are distributed to the acini. 
Describe the lymphatic supply. 
The lymphatics arising within the mucosa as blind 
canals descend to join the larger trunks in the sub- 
mucosa where the channels freely communicate with 
one another. 
Describe the nerves of the intestines. 
These are disposed in a manner almost identical with 
those of the stomach. The plexus of Auerbach and 
the plexus of Meissner are both present. 
THE LIVER. 
How is the liver developed? 
According to the type of a compound tubular gland, 
but in the mammalian adult this type is lost in the 
fusion of the tubes to form cells. 
How is the fibrous tissue arranged? 
It envelopes the exterior and is prolonged into the 
interior through the transverse fissure together with 
the blood vessels and bile ducts. 86 
GENE BAL HIS TOLOG Y. 
What is the capsule of Qlisson ? 
The prolongation of the capsule of fibrous tissue 
surrounding and separating the lobules. 
How are the blood vessels disposed? 
The inter-lobular vessels are a continuation of those 
passing through the transverse fissure and are situated 
between the surfaces of the lobules. They arc the por- 
tal vein and hepatic artery. 
Describe the portal vein. 
The portal vein gives off numerous branches which 
enter the lobule at the periphery and break up into a 
freely inter-communicating inter-lobular capillary net- 
work, the meshes of which are somewhat elongated and 
trapezoidal in form, with the smaller end directed to- 
ward the center of the lobule. A convergence to the 
inter-lobular vein in the center. 
What structures occupy the meshes of the capillary 
network ? 
Liver cells, bile capillaries and some delicate areolar 
tissue. 
Describe the liver cells. 
These possess a somewhat polyhedral form—a fine 
granular protoplasm, no cell membrane and one or 
more nuclei. Pigment granules and oil drops are usu- 
ally present. Almost all cells are bounded on at least 
one side by a capillary which does not come in direct 
contact with the cell but possesses a delicate interven- 
ing peri-vascular lymph channel. 
What is the general arrangement of hepatic tissue? 
In anastomosing cords of cells foripcd in close net- 
works. DIGESTIVE TBACT. 
87 
Where are the bile canaliculi ? 
They border the cells on all sides except on that side 
where the capillary lies. 
Describe the bile capillaries. 
These are narrow clefts found between the cells of 
the same diameter throughout the lobule; at the per- 
iphery the intercellular channels pass into the larger 
inter-lobular bile ducts, and the character of the cell 
changes from the liver cell to the low epithelium of the 
bile duct. The basement membrane becomes the con- 
nective tissue holding together the cords of the liver 
cells. 
Describe the hepatic duct. 
This is formed by the union of the inter-lobular bile 
vessels, and while the smaller ducts have no wall except 
columnar epithelium, the larger vessels possess a 
fibrous adventitia and an inner mucous membrane. 
Describe the mucous membrane. 
In addition to the columnar epithelium, it comprises 
a tunica propria of elastic fibres and some involuntary 
muscle disposed in circular and longitudinal bundles. 
Small mucous glands are also found in the larger 
canals. The columnar epithelium distinguishes the 
inter-lobular ducts from blood vessels of the same size. 
How are the veins disposed? 
The blood brought by the portal vein passes into the 
lobule at the periphery by numerous branches which 
unite to form the intra-lobular capillary network. This 
empties into the centrally placed vein which discharges 
into the sub-lobular veins—branches of the hepatic vein. 
Describe the nerves of the liver. 
The main trunks enter at the transverse fissure. The 88 
GENERAL HISTOLOGY. 
fibres are mostly non-medullated and accompany the 
hepatic artery to the periphery of the lobule. The ulti - 
mate distribution is not known. 
Describe the gall bladder. 
The walls are composed of a mucous membrane with 
some involuntary muscle and an outer fibrous coat. 
The mucosa is disposed in folds or rugae, which inter- 
lace and give a reticulated appearance to the mucous 
membrane. 
Describe the lymphatics. 
These are both superficial and deep. The superficial 
lymphatics accompany the branches of the arteries sup- 
plying the capsule. The deep lymphatics accompany 
the inter-lobular blood vessels. 
THE PANCREAS. 
How is the pancreas divided ? 
By connective tissue septa into lobes and lobules; 
the lobules in turn are composed of acini. 
What structures compose the pancreatic duct ? 
Fibrous connective tissue lined with a single layer of 
columnar epithelium. 
Describe the pancreatic duct. 
The branches of the main duct divide at once into the 
long, intermediate tubules. The walls of the main duct 
and the larger branches contain minute mucous glands. 
The columnar cells from the main duct gradually di- 
minish in height.and finally pass over into the flattened 
cells placed parallel to the long axis of the intermedi- 
ate tubules which are very long and narrow. Near the 
acini they divide and terminate abruptly. DIGESTIVE TBACT. 
89 
Describe the epithelium of the acini. 
The cells are short, cylindrical or conical cells, char- 
acterized by highly refracting granules—“zymogen 
granules”—which occupy the zone next the lumen and 
are thus distinguished from all granular cells. The 
clear, peripheral zone contains the nucleus. 
What are the bodies of Langerhans? 
Certain round or oval areas which appear lighter or 
less dense than the ordinary tissue, and are composed 
of groups of small, imperfect acini, among which ram- 
ify rich capillary networks. 
How are the blood vessels distributed? 
Similar to those of the salivary glands. 
How are the nerves disposed? 
The nerve trunks are confined to the connective tis- 
sue between the divisions of the gland. The ultimate 
termination of the fibres is undetermined. THE URINARY ORGANS. 
THE KIDNEY. 
What is the kidney? 
A highly developed compound tubular gland com- 
posed of pyramidal lobules, whose function consists 
in the secretion of urine. 
What is seen in longitudinal section ? 
Two regions are appreciable; a peripheral granular 
zone, the cortex embracing the outer third, and the 
radially striated medulla occupying the remaining 
two-thirds. 
What are the papillae? 
A number of eminences at the inner surface of the 
medulla next the pelvis at whose apices open the large 
terminal uriniferous tubules. 
What constitutes the lobules of the kidney ? 
The pyramidal mass of dividing and subdividing 
tubules, the base of which corresponds to the surface 
of the organ and its apex to the renal papillae; this 
division disappears in the adult human organ. 
What are the Malpighian pyramids? 
Striated conical structures which occupy the me- 
dulla to the number of from eight to twenty. The 
apices correspond to the papillae and their bases to 
the line of juncture betwen the cortex and medulla. 
91 92 
GENERAL HISTOLOGY, 
What produces the light and dark striae in the 
pyramids? 
The uriniferous tubules and the blood vessels re 
spectively. 
What constitute the columns of Bertini ? 
The masses of the organ extending between the 
sides of the Malpighian pyramids as far as the pelvis. 
They contain large blood vessels. 
What constitute the medullary rays or pyramids of 
Ferrein ? 
Slender tapering bundles of parallel tubules extend- 
ing from the Malpighian pyramids into the cortex. 
How is the cortex subdivided by the penetration of 
the rays? 
Into the medullary rays and the labyrinths. 
Why is the labyrinth so called? 
On account of the great tortuosity of the component 
uriniferous tubules. 
What are the dark red points irregularly placed 
throughout the labyrinth? 
Malpighian bodies. 
Of what do they consist? 
The glomerulus or Malpighian tuft and the capsule of 
Bowman. 
How are the blood vessels of the glomeruli ar= 
ranged ? 
The afferent artery breaks up into numerous capilla- 
ries united by delicate connective tissue into groups. 
The efferent collects the blood escaping from the con- 
voluted capillaries, THE URINARY ORGANS. 
93 
How Is the connective tissue distributed about the 
kidney ? 
The blood vessels of the labyrinth and the secreting 
parenchyma of the organ are enveloped in connective 
tissue, which also forms a fibrous investment of the 
organ. 
Where do the blood vessels lie as regards the cap= 
sule ? 
On the outside, the capsular wall being pushed in 
before the developing tuft. 
How is the reflected portion of the capsule disposed ? 
It closely invests the convoluted capillaries and dips 
in between the vascular lobules of the glomerulus. 
Where do all uriniferous tubules arise ? 
In the dilated capsule of Bowman in the labyrinth. 
Where is the neck? 
At the pole of the Malpighian body, opposite the vas- 
cular stalk, and is the beginning of the tubule. 
What portion of the tubule succeeds the neck? 
The proximal convoluted tubule characterized by its 
large size and tortuous course. 
Where is the spiral portion? 
This succeeds the proximal convoluted tubule; be- 
ginning about at the junction of cortex and medulla, it 
passes into the medullary ray as a slightly wavy tube 
of markedly diminished size. 
Describe the next portion. 
This is the narrowest portion of the tubule and it 
extends into the medulla as far as the papillary zone, 
being known as the descending limb of Henle’s loop. 94 
GENERAL HISTOLOGY. 
What is the next portion named? 
Henle’s loop. Just before this is reached the tube 
increases a little in size; the tube, after passing the loop, 
continues of same size through the ascending limb and 
passes once more to the labyrinth, where it continues a 
short way as the irregular tubule. 
What portion succeeds the irregular tubule? 
The distal convoluted tubule, which then passes into 
the arched collecting tubule to enter the medullary ray 
for the third time as the straight collecting tube. 
What are the tubes of Bellini ? 
The excretory ducts, visible to the naked eye, on the 
free surface of the papillae, resulting from the frequent 
union of small canals 
Describe the cells lining the capsule. 
They are a large, flattened epithelial cell, in single 
layer resembling endothelial plates seen in ordinary 
specimens as delicate spindle nuclei in profile. 
Describe the cells of the neck. 
They are low epithelial cells of the cuboid type. 
What cells clothe the proximal convoluted tubule ? 
Low columnar or cuboidal cells. The granularity 
and transparency vary with the stage of secretion. The 
outer zone of epithelium next the basement membrane 
presents the vertical striation of red epithelium. The 
epithelium of the spiral tubule presents few changes. 
What changes are found in the cells of the descend- 
ing limb of the loop? 
The change in the diameter causes the low columnar 
cells to be replaced by flattened transparent plates, THE ÜBINABY 0 EGA NS. 
95 
whose nuclei being thicker than the cell body encroach 
upon the lumen of the tube and give it a wavy appear- 
ance. 
Describe the cells of the loop and the ascending 
limb. 
They are polyhedral with flattened nuclei and faint 
striations. 
What distinguishes the irregular tubule? 
The uncertain lumen and distinctly striated epithe- 
lium. 
How are the cells of the distal convoluted tubule 
arranged ? 
Similar to the proximal, the epithelium being granu- 
lar, indistinctly separated into individual cells and pre- 
senting a striated outer zone. 
What cells line the arched collecting tubule and the 
straight collecting tubule? 
Low cuboidal transparent cells which pass into dis- 
tinct columnar cells for the remainder of the tubule. 
Describe the cells of the tubes of Bellini. 
These present a beautiful example of the simple 
columnar epithelium in the tall, transparent and clearly 
defined cells with which they are lined. These are the 
largest epithelial elements in the kidney. 
What is the course of the renal artery? 
Entering at the hilum, it passes through the sinus 
within the submucous tissue, where several small twigs 
are given off. Before entering the glandular tissue the 
renal artery forms several large branches which pass 
by oblique channels through the columns of Bertini to 
a point at the junction of the cortex and medulla cor- 96 
GENERAL HISTOLOGY. 
responding to the bases of Malpighian pyramids. Here 
they bend and form horizontal arches, from which 
spring the ascending inter-lobular cortical arteries and 
the arteriae rectae of the medulla. 
How are the cortical branches distributed ? 
Passing toward the free surface, they give off short 
curved lateral twigs to supply the afferent vessels of 
the glomeruli; here they divide into lobules of convo- 
luted capillaries, which in turn join to form the efferent 
vessels, and these soon break up into the capillary net- 
works which surround the labyrinth and medullary ray. 
At this point the networks are taken up by the inters 
lobular veins that accompany the arteries and pass to 
the pelvis, where they aid in forming the renal veins. 
What are the venae stellatae? 
The vessels that collect the blood from the peripheral 
zone of the cortex converge at certain points called 
venae stellatae, and afterwards pass into the labyrinth 
and follow the inter-lobular vessels. 
What are the arteriae rectae? 
These arteries supplying the medulla enter as straight 
vessels which divide and form rich networks reaching to 
the papillae, where the excretory ducts are surrounded 
by capillaries. 
What are the venae rectae ? 
Veins which accompany the corresponding arteries 
and empty into the large veins at the juncture of the 
cortex and medulla, 
Describe the course of the large venous trunks. 
They pass obliquely through the medulla along the 
arteries and join their fellows in the pelvis to form the 
renal veins. THE VEIN ARY ORGANS. 
97 
URETERS. 
What coats compose the ureter? 
The ureters, calices and pelvis of the kidney are 
composed of three coats, the mucous membrane, the 
muscular and fibrous coats. 
Describe the tunica propria of the mucous membrane. 
This consists of delicate, connective tissue fibres 
which, richly interspersed with cellular elements, 
pass without sharp demarcation into the submucosa. 
What epithelium covers the tunica propria? 
The so-called “transitional;” that is, a stratified, scaly 
epithelium, composed of but few layers, of which the 
uppermost is cylindrical or cubical. 
Describe the muscular coat. 
This consists of an inner longitudinal and outer cir- 
cular layer of smooth muscle fibre. The lower half of 
the ureter has an additional layer of longitudinal muscle 
bundles. 
How is the fibrous coat arranged? 
In loosely united connective tissue bundles. 
THE BLADDER. 
How many coats has the bladder ? 
The bladder also has three coats, the mucous, mus- 
cular and fibrous. 
What form of epithelium lines the bladder? 
The epithelium of the bladder resembles that of the 
ureter and pelvis of the kidney in every particular. A 
distinction from these is impossible. 98 
GENERAL HISTOLOGY. 
Describe the muscular coat 
This consists of strata of smooth muscle fibres; an 
inner and outer longitudinal layer which enclose be- 
tween them the circular layer interlaced in such a man- 
ner that their outlines are indistinct. 
Describe the muscular layers at base of bladder. 
Here the inner longitudinal layer is augmented and 
the circular layer forms the not always distinct internal 
vesical sphincter. 
What nerves supply the bladder ? 
Medullated and non-medullated fibres from the sym- 
pathetic system. 
Describe the blood vessels of the bladder. 
The muscular and mucous coats are furnished with a 
rich supply of capillary networks. 
THE URETHRA. 
Describe the female urethra. 
It is composed of a mucous and muscular coat. The 
tunica propria consists of delicate fibrous tissue with 
many connective tissue cells, and is beset with papillae, 
which are especially well developed near the meatus. 
The epithelium varies from stratified scaly to simple 
columnar. A few simple tubular glands are present. 
The muscular coat consists of an inner longitudinal 
and an outer circular coat of smooth fibres separated 
by a compact layer of fibrous tissue. 
Describe the male urethra. 
This structure is also composed of a mucous coat 
and a muscular coat. In the prostatic portion, the epi- 
thelium resembles that of the bladder; in the membra- THE URINARY ORGANS. 
nous portion it gradually becomes stratified columnar, 
which in the spongy portion is changed to simple 
columnar, while in the fossa navicularis it is trans- 
formed to stratified squamous. The tunica propria is 
rich in elastic fibres and covered with papillae, which 
are best developed in the fossa navicularis. Isolated 
branched tubular glands occur throughout the urethra. 
In the prostatic portion the muscular coat consists of 
an inner longitudinal and an outer circular layer of 
smooth fibres which gradually disappear in the spongy 
portion. The mucous membrane has a rich vascular 
supply. MALE REPRODUCTIVE ORGANS. 
PENIS. 
What structures compose the penis? 
The two corpora cavernosa and the corpus spongio- 
sum, all being enveloped by fascia and skin. 
Describe the corpus cavernosum. 
It is composed of a fibrous sheath, the tunica albu- 
ginea, and of erectile tissue. The tunica albuginea 
is a stout connective tissue membrane I mm thick 
in which an outer longitudinal and an inner circular 
layer can be distinguished; the bundles intermingle 
with many elastic fibres. The erectile tissue consists 
of connective tissue trabeculae with some smooth mus- 
cle fibres which form a network, the spaces of which 
are lined with a single layer of flat epithelial cells and 
filled with blood. The arteries in part open into capil- 
laries, and in part directly into the deep cortical plexus. 
Describe the disposition of the capillaries. 
They form a network beneath the tunica albuginea, 
called the superficial cortical plexus, which is con- 
nected with a many layered net of wide venous chan- 
nels, known as the deep cortical plexus which lies in 
the upper part of the erectile tissue and passes gradu- 
ally into the venous spaces of the latter. 
What are the helicine arteries? 
Small branches within slender trabeculae which pro- 102 
GENERAL HISTOLOGY. 
ject as loops in the cavernous spaces and appear to 
terminate in blind ends. The helicine arteries are sup- 
posed to furnish compensatory receptacles for the blood 
during extreme erection. 
How are the veins disposed? 
They arise mostly from the deep cortical plexus and 
partly from the deeper portions of the erectile tissue, 
and penetrating the tunica albuginea empty into the 
dorsal veins of the penis. 
Describe the corpus spongiosum. 
• The central portion is a venus network formed by the 
conspicuously developed veins of the urethral submu- 
cosa, while the peripheral portion resembles the struc- 
ture of the corpora cavernosa, excepting that there is 
no direct communication of the arteries with the venous 
spaces. The tunica albuginea consist of circularly ar- 
ranged bundles of fibrous tissue. 
Describe the glans. 
It consists of greatly convoluted veins held together 
by strong connective tissue, which supports the blood 
vessels. 
TESTICLE 
What is the testicle ? 
A compound tubular gland enveloped in a fibrous 
capsule, the tunica albuginea. 
What is the corpus Highmori, or mediastinum? 
A mass formed by the thickening of the capsule on 
the upper posterior aspect of the testicle. 
How is the testicle subdivided ? 
By a number of septa passing from the mediastinum MALE HE PRODUCTIVE ORGANS. 
103 
by divergent paths to the tunica albuginea on the 
opposite side. The divisions are named pyramidal 
lobes, and have the base directed toward the capsule 
and the apex toward the corpus Highmori. 
Describe the tunica albuginea. 
This structure consists of dense fibrous connective 
tissue with its free surface covered by a single layer of 
flat epithelial cells, and on its inner surface it lies in 
contact with a layer of loose connective tissue, called 
the tunica vasculosa, which connects with the inter- 
lobular septa. 
Where is the rete testis? 
This network of freely anastomosing tubules is en- 
closed by the dense fibrous tissue of the corpus High- 
mori. 
What is the interstitial connective tissue? 
Prolongations of connective tissue from the septa to 
surround the seminiferous tubules. It is rich in cellu- 
lar elements. 
How are the seminiferous tubules disposed? 
In three portions, the convoluted tubules, the straight 
tubules, and the rete testis. 
Describe the convoluted tubules. 
These are round winding canals whose origin is not 
yet determined. It is probable that they are united at 
the periphery with one another, and form a network 
from which numerous tubules turn aside and pass with 
many windings to the corpus Highmori. The walls 
are composed of several layers of flattened endothe- 
lioid connective tissue plates on a thin basement mem- 
brane, on the inside of which lies a lining of stratified 
epithelial cells. 104 
GENERAL HISTOLOGY. 
Describe the cells next the basement membrane. 
These cells are of two kinds, the sustentacular cells 
or Sertoli’s columns, which are not directly concerned 
in the production of the seminal filaments, and the 
spermatogenic cells which increase by mitosis and grow 
to be large cells that occupy a second layer just back 
of the first. These are called mother cells, and in turn 
give rise to four daughter cells, lying still nearer to the 
center of the tubule. 
Describe the spermatoblasts. 
This name is applied to the daughter cells, and from 
them the spermatozoa are directly derived. The 
nucleus of each spermatoblast develops into the head 
of a spermatozoon, a small portion of the protoplasm 
forming the caudal filament. The middle piece reacts 
like paranuclein, and probably is derived from the cen- 
trosome. 
Describe the straight tubules. 
The tubuli recti begin where the secreting portion of 
the convoluted tubules end, and a reduction in size oc- 
curs as well as in number. The walls consist of a 
membrana propria and a simple layer of low columnar 
cells. 
Describe the rete testis. 
These canals are lined with a simple stratum of cubi- 
cal or flat epithelial cells. 
Describe the vasa efferentia. 
These emerge from the upper end of the rete testis 
and form the coni vasculosi by their progressively in- 
creasing convolutions, and ultimately form the globus 
major of the epididymis. The lining cells are simple 
cylindrical epithelial elements, alternating with clusters MALE HEP BOD UCTIVE ORGANS. 
105 
of cubical cells without ciliae. A fibrous membrana 
propria and a tunic of- non-striped muscle, consisting 
of several circular strata, complete the walls 
Describe the epididymis. 
This structure possesses a stratified ciliated epithe- 
lium, and its convolutions are supported and held to- 
gether by a loose vascular connective tissue. 
Describe the vas deferens. 
This consists of either a two-layered columnar epi- 
thelium, or a transitional epithelium, of a layer of con- 
nective tissue divided into a tunica propria and submu- 
cosa, and of an inner circular and outer longitudinal 
layer of smooth muscle fibres. 
Describe the ampulla. 
This is the terminal expansion of the duct, and the 
walls are somewhat thinner. Branched tubular glands 
are formed in the mucous membrane, and the columnar 
cells contain many pigment granules. The seminal 
vesicles possess the same structure. 
Describe the ejaculatory duct. 
This consists of a simple columnar epithelium and a 
thin inner circular and outer longitudinal layer of 
smooth muscle. 
Describe the arteries of the testicle. 
They are branches of the spermatic coming partly 
from the mediastinum and partly from the tunica vascu- 
losa, and break up into capillary networks which sur- 
round the seminiferous tubules. The veins follow the 
course of the arteries. 106 
GENERAL HISTOLOGY. 
SEMEN 
What is the semen?. 
The secretion of the testicles, consisting almost en- 
tirely of spermatozoa, in which a head and tail can be 
distinguished. 
Describe a spermatozoon. 
The head is 3-5 m. long by 2-3 m. broad, and seen 
from the side appears flattened and somewhat pyriform, 
with the narrow end directed forward; from above the 
surface is oval with a rounded anterior end. 
How is the tail disposed ? 
It exhibits a delicate filament called the axial fibre, 
which is composed of delicate fibrils. It is described 
in three divisions, the middle piece lying next the head, 
the main piece and the end piece. 
Describe the movements of the spermatozoon. 
The spermatozoa are distinguished by their extra- 
ordinary vitality. The vibratile movements are exe- 
cuted by the tail, which drives the head before it. The 
movements occur generally after the dilution of the 
secretion normally effected by admixture of the fluids 
of the ampulla, the seminal vesicles, of the prostate 
and Cowper’s glands. The motion may continue for 
24 to 48 hours after death, and longer still in the secre- 
tions of the female generative tract. 
THE PROSTATE BODY. 
Describe the prostate gland. 
It consists mostly of smooth muscle fibres; the lesser 
part is glandular tissue composed of thirty to fifty sim- 
ple branched tubular glands, and is characterized by MALE REPRODUCTIVE ORGANS. 
107 
the wide intervals between the tubules which open by- 
two large and a number of smaller ducts into the 
urethra. 
Describe the cells of the tubules. 
The cells are low columnar elements which line the 
tubules in a simple layer; in the larger ducts transi- 
tional epithelium is formed, like that in the prostatic 
portion of the urethra. 
What are the prostatic crystals ? 
Round, stratified masses of secretion, up to 0. 7 mm 
in size, occurring in the tubules of elderly persons. 
The plain muscle fibres are increased toward the 
urethra and form a strong circular layer called the in- 
ternal vesical sphincter. The outside of the gland also 
shows smooth muscle fibres which extend to the bun- 
dles of striated muscle forming the external vesical 
sphincter. 
Describe the glands of Cowper. 
These also are compound tubular glands, whose wide 
tubules are covered with a simple layer of clear colum- 
nar cells, and the excretory duct is lined with two or 
three strata of cubical cells. FEMALE REPRODUCTIVE ORGANS. 
OVARY. 
How is the ovary divided for description? 
Into a cortex and medulla. 
What cells cover the free surface of the cortex? 
Low columnar cells called the germinal epithelium. 
What is included in the cortex? 
The outer third of the organ, containing the Graafian 
follicles and the ova. 
What is comprised in the medulla ? 
The inner two-thirds of the organ containing the 
blood vessels. 
What is the ovarian stroma? 
A peculiar kind of connective tissue characterized by 
its many spindle cells. It is found throughout the 
organ, but is more conspicuous as it nears the per- 
iphery. 
What is the tunica albuginea? 
A condensation of the cortical stroma recognized as 
a distinct layer directly beneath the germinal epithe- 
lium. 
Describe the immature Graafian follicle. 
The most immature follicle consists of an ovum sur- 
rounded by a single layer of flattened cells, and outside 
109 110 
GENERAL HISTOLOGY, 
of these lie the cells of the stroma, with no intervening 
membrane. Others more advanced are present, with 
two or more rows of polygonal cells. 
What is the origin of the cells surrounding the 
ovum? 
They arise from the germinal epithelium as cylindri- 
cal masses which penetrate the stroma and proliferate, 
thereby forming numerous elements within the follicle. 
Describe the mature Graafian follicle. 
These appear as clear vesicles 4-8 mm in diameter 
and differentiated from the surrounding tissue by a 
condensation of stroma forming a sheath—the theca 
folliculi. 
Describe the theca folliculi. 
It is composed of two layers, an outer, the tunica 
fibrosa, comprised of fibrous connective tissue and 
coarser blood vessels, and an inner tunic propria, rich 
in cells and capillaries. 
Describe the membrana granulosa. 
Consisting of many layers of small polyhedral cells, 
it is the product of the single row of cells originally 
surrounding the ovum. 
What is the discus proligerus ? 
This term is applied to a thickening of the membrana 
granulosa which continues as a zone of cells surround- 
ing the ovum The cells lying next to the ovum are 
placed vertically to its surface, forming a radical zone 
called the corona radiata. 
What is the liquor folliculi ? 
An albuminous fluid filling the interior of the follicle 
and derived as exudate from the blood vessels of the FEMALE BEPBOD UGTIVE ORGANS. 
theca, and partially from the destruction of the central 
cells of follicle. 
Where is the ovum ? 
This is a spherical body about 2 mm in diameter, 
lying within the discus proligerus and surrounded by a 
distinct membrane—the zona pellucida. 
Describe zona pellucida. 
This structure is derived from the cells of the discus 
proligerus and forms a protecting membrane present- 
ing a delicate radial striation. 
What is the vitiline membrane ? 
Lying next to the zona pellucida, it limits the proto- 
plasm of the ovum and forms a true but inconspicuous 
cell wall. 
Describe the protoplasm of the ovum. 
Composed of albuminous matter, it is modified by the 
presence of numerous fatty particles. 
Describe the germinal vesicle. 
This structure corresponds to the nucleus of the ovum, 
and is situated eccentrically, limited by a distinct mem- 
brane,and contains the nucleolus or germinal spot. It 
is within the germinal vesicle that the important 
changes of cell division are inaugurated. The chroma- 
tin threads form a loose network throughout the vesi- 
cle, the inner spaces being filled with a substance rep- 
resenting the nuclear juice. Sometimes the follicle 
contains more than one ovum. 
Describe the medulla. 
This is characterized by the looseness of its structure 
and the size of its vessels. The stroma of the medulla 
contains more fibrous tissue, fewer spindle cells and 112 
GENERAL HISTOLOGY\ 
some involuntary muscle separating and surrounding 
the vessels, which are largely venous. 
What are interstitial cells? 
These are polygonal epithelial cells and represent 
the remains of the cylindrical cell masses which grow 
into the tissue of the primitive ovary from the Wolffian 
body. They are found in groups between the bundles 
of stroma in the cortex and medulla. 
Describe the corpus luteum. 
This is produced by changes in the ruptured and 
partly collapsed follicle, which becomes filled with 
blood after the escape of the ovum. Gradually a mass 
of polyhedral cells forms and capillaries from the folli- 
cular vessels extend into the mass, which afterwards 
shrinks and is later invaded by the peripheral cells. It 
follows the discharge of every mature ovum, and when 
pregnancy occurs it becomes exceptionally large and 
retains its distinctive character much longer. 
Describe the blood vessels of the ovary. 
They enter at the hilus, penetrate to the medulla and 
give off twigs to supply cortex and Graafian vesicles. 
What nerves supply the ovary ? 
Both cerebro spinal and sympathetic systems send 
fibres to the ovary, and both pale and medullated fibres 
are present. 
PAROVARIUM. 
Where is the parovarium ? 
It lies transversely within the broad ligament between 
the ovary and oviduct. 
Of what does it consist ? 
A group of tubular structures whose vertical tubules FEMALE REPRODUCTIVE ORGANS. 
113 
converge somewhat at their ovarian ends, and their op- 
posite ends are connected with a longitudinal head tube 
of larger caliber which extends downward into the 
broad ligament. 
What cells line the tubules ? 
Low columnar epithelial cells. 
What is the origin of the parovarium ? 
It represents the remains of parts of the Wolffian 
body—the transverse tubules corresponding to the 
tubules of the body, while the head tube is identical 
with the upper part of the Wolffian duct—when this 
tube persists for any great part of its original length it 
is called Gartner’s duct. 
What is the stalked hydatid of Morgagni? 
This is a pedunculated vesicle, representing the re- 
mains of the duct of the pronephros and is found in 
both sexes. Its dilated sac and stalk when pervious are 
lined with low columnar or cuboidal epithelium. 
FALLOPIAN TUBE. 
What coats comprise the Fallopian tubes? 
The mucous, muscular and serous. 
How is the mucous membrane arranged ? 
In numerous longitudinal folds that give the trans- 
verse section a stellate appearance. There are no 
glands in the mucous membrane of the oviduct. 
What composes the mucous coat ? 
A fibro-elastic tunica propria containing numerous 
connective tissue cells and a layer of ciliated, simple 
columnar epithelium, the ciliary wave being directed 
toward the uterus. 114 
GENERAL HISTOLOGY. 
What lies outside the tunica propria ? 
An extremely thin muscularis mucosae, consisting of 
longitudinal bunches of smooth muscle. 
Describe the submucosa. 
This is only represented by a thin layer of fibrillar 
connective tissue. 
Describe the muscular coat. 
This consists of an inner circular and an outer, very 
thin, longitudinal layer of smooth muscle. 
Describe the serous coat. 
This coat is formed by the peritoneum and a consid- 
erable layer of loose bundles of connective tissue. 
Describe the blood vessels. 
They form a narrow meshed and abundant capillary 
network. The larger veins run along the bases of the 
longitudinal folds of the mucosa. 
THE UTERUS. 
What coats are found in the uterus? 
Mucous, muscular and serous. 
Describe the muscular coat. 
Although composed of smooth fibres that interlace 
in all directions, three layers are distinguished: an in- 
ner layer having mostly a longitudinal direction, a 
middle layer having in general a circular direction, 
called the stratum vasculare (on account of the numer- 
ous arteries and veins), and an outer layer (stratum 
supra-vasculare) formed partly of circular bundles and 
partly of longitudinal bundles. FEMALE REP FOB VOTIVE ORGANS. 
115 
Describe the muscle fibres. 
They are elongated spindle cells, or blunted and 
frayed at the ends and sometimes forked. They vary 
from 60—600/ a in length. The nucleus, sometimes mul- 
tiple, is usually oval and lies in a granular substance. 
How is the mucosa divided for description? 
As follows: 
The virgin mucosa resting. 
The mucosa menstruating. 
The mucosa of the gravid uterus. 
Describe the virgin mucosa resting. 
After puberty it has a thickness of from 1-2 mm and 
is covered by a single layer of ciliated columnar cells, 
the ciliary wave being directed toward the cervix. The 
tunica propria is formed of fine fibrous tissue resemb- 
ling embryonic connective tissue and consisting of 
elongated cells with oval nuclei. The cells send out 
branched processes in all directions, which unite with 
those of neighboring cells, and form a cellular network, 
the meshes of which are occupied by leucocytes and 
lymph. The tunica propria supports the simple or 
forked gland tubules which not infrequently extend to 
the muscularis. The glands are invaginations of epi- 
thelium, and consist of a simple layer of ciliated epi- 
thelium resting on a delicate basement membrane com- 
posed of anastomosing connective tissue cells. The 
arteries run in a spiral course from the muscularis to 
the surface of the mucous membrane, where they break 
up into capillaries and form a close network. The 
veins leading from the capillaries form a plexus in the 
deeper layers of the mucosa. In the cervix, the mucous 
membrane is thicker, and its upper two-thirds is cov- 116 
GENERAL HISTOLOGY. 
ered with a single layer of tall ciliated cells. Near 
these stratified squamous cells appear. 
Where are the mucous crypts ? 
Mucous follicles occur also in the membrana, of the 
cervix and some few scattered tubular glands. 
What changes are noted during the period of men= 
struation ? 
Thickening of mucosa and structural changes, men- 
struation, regeneration. 
Describe the initial phase 
This is characterized by considerable thickening of 
the mucosa, the surface becomes irregular, the mouths 
of the glands open in deep depressions, the blood ves- 
sels become enormously enlarged. The thickening of 
the mucosa depends somewhat on actual increase of 
tissue from the proliferation of connective tissue cells 
and leucocytes and by growth of gland tubules. This 
condition of the mucosa is called decidua menstrualis. 
Then follows disintegration of the upper layer of the 
mucosa and infiltration of blood into the subepithelial 
tissues; the enlarged blood vessels become exposed 
and rupture, causing hemorrhages into the uterine cav- 
ity, and the flow into the vagina which constitutes the 
external signs of menstruation. The surface now being 
devoid of epithelium consists of connective tissue and 
exposed blood vessels. 
Describe the stage of regeneration. 
The hyperaemia disappears rapidly, the effused blood 
is partly absorbed and partly cast off, a cellular net- 
work grows upward and restores the lost tunica propria 
while the epithelial covering of the mucosa is regener- 
ated from the gland cells. FEMALE EEPEODUCTIVE OEGANS. 
117 
How does the mucous membrane appear at different 
depths ? 
The superficial zone is compact, and the deep zone 
shows numerous cavities produced by the lower di- 
visions of the gland tubules which have become 
widened and tortuous. Later on the channels of the 
glands appear compressed and straightened, owing to 
the distension of the uterus. Between the glands are 
many blood vessels, spindle cells and multi-nucleated 
giant cells. The epithelium of the glands is soon lost 
and the gland lumina become adherent and are obliter- 
ated. 
How is the decidua gravitatis divided for descrip- 
tion ? 
The mucosa of the gravid uterus is considered under 
three heads. 
The decidua serotina, when the ovum finds attach- 
ment. 
The decidua vera, which comprises all the mucosa 
attached to the uterus not comprised in the above. 
The decidua reflexa, or that portion of the mucosa 
that encapsules the ovum (it disappears about the 
fifth month). 
The decidua vera and serotina develop throughout 
the pregnancy much as the menstrual decidua, but the 
progressive alterations assume vastly greater propor- 
tions. 
Describe the decidual cells. 
These are flattened spherical oval or branched cells 
of conspicuous size, which occur in large numbers in 
the mucosa of the gravid uterus. Usually they possess 
but one nucleus, but sometimes multiple nuclei are 
present. Late in pregnancy they assume a brownish 118 
GENERAL HISTOLOGY. 
color. They are found more numerously in the upper 
compact zone of the serotina. The decidual cells are 
said to arise from connective tissue elements. 
Describe the chorion and amnion. 
These fcetal membranes are seen in cross sections of 
the decidua vera loosely united by mucous connective 
tissue. The chorion consists of an epithelial and a con- 
nective tissue layer, of which the first is turned toward 
the uterine wall, and the latter toward the amnion. In 
the amnion the epithelial layer of cubical cells is turned 
toward the cavity of the uterus, and the connective tis- 
sue layer faces the chorion. 
Describe the lymph vessels. 
They form a wide meshed network in the mucosa, 
provided with blind branches, and send small twigs 
through the muscularis to connect with a close subser- 
ous network of larger channels. 
Describe the nerves of the uterus. 
They are both medullated and non-medullated, and 
branching in the muscularis they form a dense plexus 
here and in the mucosa. 
VAGINA AND GENITALS. 
What coats are formed in the vagina? 
Mucous, muscular and fibrous coats. 
Describe the mucous membrane. 
It is composed of stratified scaly epithelium and a 
tunica propria beset with papillae which are built up of 
small interlacing bundles of connective tissue mingled 
with elastic fibres and leucocytes. The mucosa rests 
on a submucosa consisting of loose bundles of tissue FEMALE REPRODUCTIVE ORGANS. 
119 
and robust elastic fibres. There are no glands in the 
mucosa of the vagina. 
Describe the muscular coat. 
This is composed of an inner circular and an outer 
longitudinal layer of smooth muscle fibres. 
Describe the fibrous coat. 
This is composed of dense connective tissue mingled 
with elastic fibres. 
Describe the blood and lymph vessels. 
These are arranged in parallel horizontal networks in 
the submucosa and tunica propria. The venous channels 
lie between the bundles of the muscular coat. The 
nerves form a plexus with many small ganglia in the 
outer fibrous coat. 
What characterizes the mucosa of the external gen= 
iatalia ? 
It possesses numerous glands, and on the labia minora 
sebaceous glands without hair follicles are found. The 
labia majora possess the same structure as the skin. RESPIRATORY SYSTEM. 
What is comprehended in the respiratory tract? 
The system of air passages, such as the nasal fossae, 
pharynx, larynx, trachea and bronchial tubes, and the 
special organs of respiration, the lungs. 
THE LARYNX. 
What is the structure of the larynx? 
A cartilaginous framework formed by the thyroid, 
cricoid, arytenoid, and the other smaller cartilages of 
Wrisberg and Santorini, united by ligamentous mem- 
branes and fibrous tissue and lined by mucous mem- 
branes; on the outside the cartilages are covered by 
fibrous and mucous structures. 
What constitutes the mucous membrane ? 
An epithelium, a tunica propria and a submucosa. 
What is the character of the epithelium ? 
That covering the epiglottis and the laryngeal cavity 
as far as the false vocal cords is stratified, squamous— 
at the lower edge of the false vocal membranes it be- 
comes stratified ciliated columnar and extends through- 
out the laryngeal ventricle. On the true vocal cords, 
the epithelium is again stratified, squamous and beyond 
this the bronchial type continues—stratified ciliated 
columnar. 
121 122 
GENERAL HISTOLOGY. 
What elements compose the tunica propria? 
Fibrous connective tissue with a rich network of 
elastic fibres, and the superficial part is beset with 
papillae. 
Describe the true vocal cords. 
The vocal cords are folds of the mucosa, composed 
principally of longitudinal bundles of elastic fibres, 
some fibrous tissue, covered by stratified squamous 
epithelium and externally reinforced by fasciculi of the 
muscle. They have no mucous 
glands. 
Describe the epiglottis. 
The epiglottis is composed principally of yellow 
elastic cartilage. Numerous taste-buds, similar to 
those on the tongue, lie embedded in the posterior sur- 
face and leucocytes are numerous so that the mucosa 
assumes the aspect of diffuse adenoid tissue. The 
minute glands lie embedded in the pits and openings 
in its plate of cartilage. 
Describe the submucosa. 
This is a loose tissue that serves to unite the mucous 
membrane with the firmer surrounding structures; in 
places mucous follicles are found lined with columnar 
cells. 
What cartilages are hyaline ? 
The thyroid, cricoid and arytenoid. 
What cartilages are yellow elastic? 
The epiglottis, the apex and processus vocales of the 
arytenoid and the cartilages of Wrisberg and Santorini. 
What are the cartilagines trilicse? 
Little nodules embedded in the lateral thyro-hyoid RESPIRATORY SYSTEM. 
123 
ligaments and are composed sometimes of fibrous and 
sometimes of yellow elastic cartilage. 
How do the blood vessels terminate? 
Within the mucosa in capillary networks beneath the 
epithelium and in the papillae by vascular loops. 
How are the lymphatics arranged? 
As a superficial network within the mucosa and a 
deeper set within the submucous tissue, the largest be- 
ing found on the anterior surface of the epiglottis. 
What kind of nerves supply the larynx? 
Principally medullated fibres, although pale fibres are 
sometimes present. 
THE TRACHEA. 
What is the general structure of the trachea? 
A fibrous tube, lined with mucous membrane and kept 
patulous by incomplete cartilaginous rings. 
Describe the epithelium of the mucous membrane. 
The epithelium is of the stratified ciliated columnar 
variety, and among the elements lie goblet cells. The 
current established by the ciliae tends to expel mucous 
or other substances. 
Wherein is the tunica propria conspicuous? 
For its large amount of elastic tissue. 
How is it distributed ? 
In two zones: an inner loose, fibrous layer containing 
a small amount of elastic fibres, vascular loops, nerve 
fibres and lymphoid cells, and an outer layer, next to 
the submucosa, composed of a close network of longi- 
tudinal elastic fibres. 124 
GENERAL HISTOLOGY. 
How is the submucosa arranged? 
This is a loose structure and connects the mucosa 
with the fibrous sheath and supports the glands, lym- 
phatics, nerve trunks, and larger blood vessels. 
Describe the tracheal glands. 
These are racemose glands occupying the submucous 
layer and connecting with the surfaces by long, excre- 
tory ducts. They are lined with low columnar epithe- 
lium, while the acini contain cuboidal cells. 
Where is the fibrous coat? 
External to the submucosa, and forms an investment 
in which the cartilaginous rings are embedded. 
Describe the rings of cartilage. 
These are masses of hyaline cartilage of horse-shoe 
shape, embracing about three-fourths of the tracheal 
tube. 
How is the remaining space bridged? 
By the fibrous tunic and a layer of transversely dis- 
posed bundles of non-striped muscle which extend 
along the inner side of the cartilages to whose peri- 
chondrium they are attached. 
How are they otherwise distributed? 
Across the intervals between the rings, thus forming 
a continuous layer that serves to contract the tube 
Longitudinal muscular bands are also present. 
Describe the blood supply. 
The larger blood vessels pass to the submucosa, from 
which smaller twigs are given off to supply the mucous 
membrane and partially the fibrous and cartilaginous 
structures. RESPIRATORY SYSTEM. 
125 
How do the vessels terminate ? 
In a network within the mucosa beneath the epithe- 
lium, The acini of mucous glands are surrounded by 
capillaries. 
Describe the lymphatics. 
Lymphatics are numerous within the mucous and 
submucous coats. Lymphoid tissue in the form of 
solitary follicles also occurs. 
Describe the nerves. 
Both the medullated and non-medullated fibres occur. 
The larger trunks pass into the submucosa and send 
out minute fibrillae. 
THE BRONCHI. 
How do the bronchi differ from the trachea? 
The large bronchi have almost exactly the structure 
of the trachea, but the smaller tubes are modified to 
conform to the gradual reduction in size. 
How is the epithelium modified ? , 
It is reduced to a single layer of ciliated columnar 
cells. 
How is the mucosa affected? 
At first it is not greatly diminished, as the loss in 
elastic tissue is compensated for by the appearance of 
an additional layer of smooth muscle between the mu- 
cosa and submucosa. 
Describe the muscular layer. 
It corresponds to a muscularis mucosae, and forms a 
complete investment, especially conspicuous when the 
cartilaginous plates diminish. 126 
GENEBAL HISTOLOGY. 
How do the ring cartilages disappear? 
At first reduced in size, they are broken up and 
finally replaced by irregular short plates which, becom- 
ing smaller and more infrequent, disappear entirely in 
the smaller bronchioles. 
What is the smallest bronchiole named? 
When the bronchiole does not exceed one millimeter 
in diameter, it is called a terminal bronchus. 
How does a terminal bronchus end ? 
In slightly larger alveolar passages, the walls of 
which are studded with air sacs, from which extend 
blind, irregular spaces called infundibula, which are 
surrounded by air sacs communicating with the general 
cavity, but not with each other. 
What cells line the terminal bronchioles? 
Ciliated epithelium. 
What cells line the alveolar ducts? 
Cuboidal cells which rapidly assume a flat polygonal 
type. 
Describe the walls of a terminal bronchus. 
Outside the single layer of epithelium is the mucosa 
containing longitudinal elastic fibres and thin irregular 
annular bundles of smooth muscle. The mucous 
glands and cartilaginous plates are absent. 
Describe the walls of the alveolar ducts. 
These show still further reduction, the fibrous coat is 
greatly thinned, and the mucous coat becomes a deli- 
cate tunica propria of fibro-elastic tissue wherein 
some smooth muscle fibres remain, RESPIRATORY SYSTEM. 
127 
Describe an infundibulum. 
It is lined with large flat endothelial plates between 
which smaller polygonal cells appear. 
THE LUNGS. 
How do the lungs resemble racemose glands? 
In plan of development the bronchial tubes corre- 
spond to excretory ducts and the pulmonary parenchy m a 
to glandular tissue. 
What structures comprise the pulmonary parenchy 
ma? 
Groups of air sacs, enclosed by connective tissue, 
form lobules, which in turn are united into lobes, and 
all are connected by alveolar tissue. 
Describe the air sacs or alveoli. 
These correspond to the acini of racemose glands, 
and are placed closely side by side, the mutual pres- 
sure making them polyhedral. They open into the 
common passages of the alveolar ducts and infundibula, 
and around the opening, the elastic tissue of the infun- 
dibulum is arranged as a ring from which the electric 
fibres pass in all directions over the sac to form its 
framework. 
What does the wall of the air sac comprise ? 
The epithelium, connective tissue framework and 
capillary network. 
Describe the epithelial lining. 
This is composed of a single layoff of large plates 
similar to endothelium, among which small polygonal 
cells lie scattered. 128 
GENERAL HISTOLOGY. 
What is the order of appearance of these cells? 
The small cells only are present in the embryonal 
condition, but after inflation has occurred the large cells 
appear. 
What are stomata? 
Minute openings frequently found at the junction of 
the angles between the cells and connecting with the 
lymphatics. 
What Is the framework of the air sac composed of ? 
Principally of elastic fibres from the annular bundle 
surrounding the mouth of the sac, some fibrous tissue 
and a few connective tissue cells. 
How is the framework arranged ? 
It completely surrounds the alveolus and constitutes 
the septum between adjoining air sacs, and acts as a 
support for the capillary vessels and the investing epi- 
thelium. 
Describe the capillary network. 
This is remarkable for the closeness of its meshes. 
The smaller twigs extend among the groups of infundi- 
bula, embracing the opening into the air sacs with 
more or less complete rings from which pass the capil- 
laries enveloping the air sacs with network on all sides. 
How are they disposed between the alveoli ? 
Between the alveoli only a single layer of capillary 
vessels is present, and they encroach alternately upon 
the adjacent air sacs as projecting arches or loops. 
How are the alveoli of different infundibula sepa= 
rated ? 
By distinct connective tissue partitions which in- 
crease in thickness as the included pulmonary sub- RESPIRATORY SYSTEM. 
129 
stance becomes larger, until they become the fibrous 
envelope ensheathing the lobes. 
How are the lymphatics arranged? 
In two sets, one of which arises in the connective tis- 
sue septa, and the other in connection with the bron- 
chial mucous membranes. 
What nerves supply the lungs ? 
The cerebro-spinal and sympathetic systems both 
contribute fibres to the lungs. 
THE PLEURA. 
What tissues compose the pleura ? 
An endothelium, covering a connective tissue matrix, 
and a subpleural tissue. 
Describe the endothelium. 
It comprises a single layer of large, thin, irregular 
polyhedral connective tissue plates, between the junc- 
tures of which minute stomata are frequently found. 
Describe the connective tissue matrix. 
This consists of fine bundles of fibrous connective tis- 
sue, intermingled with elastic fibres. 
How are the lymphatics disposed ? 
The inter-communicating lymph channels form a 
plexus of considerable richness within the fibrous lam- 
ellae. 
Describe the subpleural tissue. 
Where developed as a layer of some thickness, it is 
composed of loosely disposed areolar tissue containing 
many elastic fibres. SKIN AND APPENDAGES 
What elementary structures compose the skin ? 
A superficial epithelial layer, the epidermis, derived 
from the ectoderm, and a deeper connective tissue layer 
—the corium—derived from the mesoderm. 
What cells compose the epidermis? 
Highly developed squamous epithelium, which forms 
an accurately fitting protective covering over the entire 
body surface. 
How are the cells arranged ? 
In irregular layers, dependent upon the cuticular de- 
velopment. 
What layers can be distinguished in well developed 
skin ? 
The stratum Malpighii, stratum granulosum, stratum 
lucidum and stratum corneum. 
Describe the stratum flalpighii. 
This contains the most recent and most actively 
growing elements, the deepest of which possess a dis- 
tinctly columnar character. They are bounded below 
by a thin basement membrane. 
What are the prickle cells ? 
The next layer of cells have fine intercellular clefts 
or channels bridged across by intercommunicating fi- 132 
GENHBAL HISTOLOGY. 
bres that suggest the name. There are several layer, 
of the prickle cells. 
Describe the stratum granulosum. 
The cells of the prickle layer gradually become flat- 
tened and compressed and filled with granular particles 
called eleidin, which has an affinity for carmine; this 
constitutes the granular layer. 
What is the next layer called? 
The next layer appears as an ill-defined narrow zone 
of cells which as yet is incompletely transformed into 
horny substance and is known as stratum lucidum. 
Describe the corneous layer. 
The corneous layer is composed of thin, dry, com- 
pressed plates which contain keratin and from which 
the nuclei have disappeared. 
Describe the pigment granules. 
When present these granules are especially numer- 
ous in the deeper layers of the stratum Malpighii, where 
it is conveyed by the wandering cells. 
What is the corium? 
The true skin consists of a felt work of white fibrous 
connective tissue bundles in which elastic fibres and 
smooth muscles are mixed in varying amounts. 
What two layers constitute the corium ? 
The stratum papillare and stratum reticulare. 
Describe the papillae. 
The elevations consist of closely arranged bundles of 
fibro-elastic tissue and support vascular loops and a 
rich terminal nerve supply. They vary in size, number 
and disposition in various parts of the body, being most SKIN AND APPENDAGES. 
133 
numerous and best developed on the flexer surfaces of 
hands and feet. 
What purpose do the papillae serve? 
They greatly extend the sensory surface and form 
the principal organs of tactile sensibility. 
How are the papillae disposed ? 
Upon the hands and feet they are distributed in char- 
acteristically arranged rows, which form elaborate and 
individually distinct ridges on the skin, which remain 
unchanged through life. 
What is the shape and size of the papillae? 
They have a conical figure, rounded or blunt at the 
top, and sometimes cleft into two or more points, when 
they are called compound papillae. On the palm, sole 
and nipple they are mostly compound, and measure 
from 1-200 to I-100 of an inch in height; sometimes 
they are less than i-800 of an inch in height. 
Describe the subcutaneous stratum or stratum reti- 
culare. 
This is a framework of loosely disposed fibro-elastic 
bundles continued from those of the deeper layers of 
the corium without interruption. 
What is the panniculus adiposus ? 
A compact layer composed of interfascicular spaces 
which are filled with adipose tissue. 
What are the cellular elements of the subcutaneous 
tissue ? 
The usual connective tissue cells, fusiform and plate 
like elements, leucocytes, and fat cells. The latter are 
jjQipetiiries absent. 134 
GENERAL HISTOLOGY 
What is included under appendages of the skin ? 
The nails, hair and cutaneous glands. 
Of what does the nail consist ? 
Of a large exposed body which ends anteriorly in a 
free edge and extends posteriorly as the root some dis- 
tance beneath the overhanging upper margin of the 
groove or nail fold receiving the root. The borders of 
the nails are covered by the nail walls. 
What is the appearance of the nail root? 
It is usually light in color and somewhat opaque; on 
the thumb it extends beyond the nail fold as a pale, 
projecting convex area called the lunula. 
Upon what does the nail rest? 
Upon a highly vascular and sensitive “nail-bed,” the 
posterior portion of which, covered by the root of the 
nail, is called the matrix. 
How does growth of the nail take place ? 
From the matrix alone, each newly formed increment 
pushing before it the already formed parts at the rate 
of about i mm per week The transformation of the 
cells into horny plates takes place only on the matrix. 
What is comprised in the nail=bed? 
The corium and that part of the epidermis corre- 
sponding to the stratum Malpighii. 
What are the longitudinal ridges? 
Minute elevations which occupy the surface of the 
corium, except posteriorly over the matrix. They are 
lowest behind and gradually increase in height toward 
the front of the nail, abruptly terminating when the 
nail parts from its bed. SKIN AND APPENDAGES. 
135 
Where does the epithelial portion of the nail bed 
arise ? 
From cells belonging to the stratum Malpighii. 
What is the substance of the nail ? 
Intimately united lamellae of horny epithelial cells 
possessing a nucleus and closely resembling the ele- 
ments of the stratum lucidum. 
THE HAIR. 
Whence do the hairs arise? 
Entirely from the epidermis and are, therefore, of 
ectodermic origin. 
How are hairs divided for description? 
Into the root and the shaft. 
How does the root terminate? 
In a bulbous expansion, the hair bulb, which at its 
lowest point is indented to receive the connective tissue 
papillae. 
What is the follicle? 
A pocket of modified integument in which the bulb 
is embraced; the corium and epidermis contribute re- 
spectively the fibrous and epithelial root sheaths. 
Of what does the hair consist? 
Entirely of epithelial cells disposed in three distinct 
strata called the cuticle, the cortical substance, and the 
medulla or pith. 
Describe the cuticle. 
It is composed of a single layer of thin, horny imbri- 
cated scales enveloping the entire surface of the hair. 
Owing to the imbricated arrangement only the free 136 
GENERAL HISTOLOGY, 
projecting edges are visible, and this gives the oblique 
transverse markings so distinctive of the surface view 
of hair. 
Describe the cortical substance. 
This constitutes by far the greater part of the hair, 
and is composed of elongated, horny epithelial cells, 
with attenuated nuclei, and are so intimately united 
that the boundaries of the elements are usually indis- 
tinguishable. 
What changes are found in the cells on the root ? 
They are broader and less horny, and around the 
papilla the cells of the cortical substance become con- 
tinuous with the extension of the stratum mucosum. 
Describe the medulla? 
This occupies the central part of the shaft and some- 
times extends from near the bulb to the extremity of 
the hair. 
What composes the medulla? 
Irregular cuboidal or spherical cells 15-20,0, in diame- 
ter, filled with dark granules which are really minute 
air vesicles. By reflected light the pith appears sil- 
very white, while by transmitted light it is opaque. 
Upon what does the color of the hair depend ? 
Upon the presence of pigment granules, diffuse pig- 
ment and air. 
How is the pigment distributed? 
In dark hair the granular pigment, occurring as col- 
ored particles, lies within the elements of the cortical 
substance and often between the cells. The cortex 
sometimes also contains diffuse soluble coloring mat- 
ter in combination with the cell protoplasm. SKIN AND APPENDAGES. 
137 
Describe the hair follicles. 
They are tubular or flask shaped depressions in the 
skin which tightly embrace the hair shaft. 
What is the purpose of the follicle ? 
It supplies the tissue from which the hair is formed, 
and affords the necessary attachment and support to 
the. hair after development. 
How does the follicle develop ? 
By an ingrowth of the epidermis into the subjacent 
connective tissue. The hair appearing as the result of 
the differentiation of the cells in the most dependent 
part of the epidermal plug. 
What coats comprise this hair follicle? 
Below the sebaceous glands the follicle consists of 
the fibrous coat and stratum mucosum only, but above 
the glands the stratum corneum is added. 
Describe the fibrous coat. , 
This consists of three layers—the outer of longitudi- 
nally placed bundles of connective tissue rich in cells, 
the middle of circular connective tissue, and the inner 
a clear, homogeneous zone, the hyaline membrane sep- 
arating the epithelium from the fibrous tissue. 
How is the epithelial layer disposed ? 
In two well marked strata, the outer root sheath and 
the inner root sheath. 
Describe the outer root sheath. 
This is a direct continuation of the stratum mucosum 
of the adjacent skin, and its structure corresponds with 
that layer of the epidermis. 
How are the cells disposed ? 
A layer of columnar cells lies in contact with the 138 
GENERAL HISTOLOGY. 
glossy membrane, while the succeeding layers are 
squamous epithelium. 
Describe the inner root sheath. 
This is composed of two layers, the first of which, 
Henle’s layer, consists of a single or double row of epi- 
thelial cells without nuclei, while the inner or Huxley’s 
layer is formed of nucleated cells and is lined by a 
delicate membrane, the cuticle of the root sheath, 
which exhibits the same structure as the cuticle of the 
hair. 
Describe the base of the hair follicle. 
This presents a deep invagination for the reception 
of the hair papillae containing the pigment cells and 
the blood vessels. 
GLANDS OF THE SKIN. 
What glands are found in the skin ? 
The sebaceous and sudoriparous glands. 
Describe the sebaceous glands. 
These are either branched or unbranched simple sac- 
cular glands, and consist of short excretory ducts and 
acini. 
Describe the cells of the gland. 
The duct is lined by stratified epithelium, consisting 
at first of low cuboidal cells followed by spherical or 
polyhedral elements. 
What is the sebum ? 
A semi-fluid substance consisting of oil droplets and 
the debris of broken down cells which the glands se- 
crete. SKIN AND APPENDAGES. 
139 
Where are the sebaceous glands found ? 
They are always located in the papillary layer of the 
skin, and are of universal occurrence. 
What are the sweat glands ? 
Modified, simple tubular glands, extending from the 
free surface of the skin to the deepest part of the retic- 
ular layer of the corium. They are divided for de- 
scription into two parts, the excretory duct and the 
coil. 
Describe the excretory duct. 
The duct runs a straight or sinuous course through 
the corium, enters the epidermis between two papillae, 
passes in a spiral through the corneous layer, and opens 
on the surface of the skin by a rounded orifice, the 
sweat pore just visibe to the naked eye. The walls con- 
sist of longitudinal bundles of fibrous tissue, lined 
within by several layers of cubical and epithelial cells. 
Describe the coil. 
This is a greatly convoluted simple canal lined with 
a simple layer of cuboid cells containing granules of 
pigment and fat surrounded by a delicate membrana 
propria. Sometimes longitudinal fibres of smooth 
muscle occur between the membrana propria and the 
gland cells. 
Describe the secretion. 
Usually an oily, fluid substance, under the influence 
of altered innervation it becomes the watery liquid 
called sweat. 
What glands are described with the sweat glands ? 
The ceruminous glands of the ear. The glands of 
Moll of the eyelid must be regarded as modified sudor- 
iparous glands, as they closely correspond in structure. CENTRAL NERVOUS SYSTEM* 
What constitutes the central nervous system? 
The spinal cord and the brain. 
Of what does the spina! cord consist? 
Of white and gray substance. 
How is the white substance disposed ? 
It encircles the gray matter and is partially divided 
by a deep anterior cleft, the anterior median fissure and 
a posterior septum, into a right and left half. 
How is each half subdivided? 
By the furrows marking the exit of the anterior and 
posterior roots of the spinal nerves into a large lateral 
column, an anterior column and a posterior column. 
What arrangement is peculiar to the upper thoracic 
and lower cervical region ? 
Here two divisions can be distinguished in the pos- 
terior column, of which the median portion is named 
the Column of Goll and the lateral portion the Column 
of Burdoch. 
How are the anterior columns united? 
By the white commissure at the bottom of the an- 
terior median fissure. 
Describe the gray substance. 
This appears in cross sections in the form of an H 
141 142 
GENERAL HISTOLOGY. 
and consists of two lateral columns connected by a 
horizontal bridge, the gray commissure. 
How are the columns divided ? 
Into anterior, posterior and lateral cornua. 
How are the spinal nerve roots arranged? 
The anterior roots emerge from the front boundary 
of the anterior cornua, and the posterior roots enter at 
the postero-median side of the posterior cornua. 
What is the reticular process? 
A net-like mass of gray substance found laterally at 
the base of the posterior cornua. 
Where is the column of Clark ? 
On the median side of the posterior cornua, near the 
gray commissure. 
Where is the substantia gelatinosa? 
This covers the posterior horn and immediately sur- 
rounds the central canal. 
Where is the central canal ? 
In the midst of the gray commissure. 
Where is the substantia gelatinosa Rolandi? 
This is the mass that caps the posterior horn and 
just posterior to this is the zona spongiosa, on the 
dorsal edge of which lies the zona terminalis—an area 
of cross-sectioned thin nerve fibres. 
How large is the central canal? 
From 0.5 mm to 1 mm in diameter, but not infre- 
quently it is impervious. 
How is the gray commissure divided with regard to 
the canal? 
The portions in front and behind the canal are named CENTRAL NERVOUS SIN TEAL 
respectively the anterior and posterior gray commis- 
sures. 
What are septula medullaria? 
Processes of gray matter of variable size that radiate 
into the white substance. 
What is the conus medullaris ? 
This is the end of the cord and consists almost wholly 
of gray matter. 
What is the minute structure of the gray substance? 
It consists of multipolar ganglion cells which, with 
their ramifying and axis cylinder processes, form a 
dense network—the “nerve-felt,” which is penetrated 
by nerve fibres proceeding in part from the white 
columns and in part from the posterior roots, and the 
whole is supported by a framework of neuroglia. 
How are the nerve cells divided? 
In accordance with the relations of their axis cylinder 
processes into motor cells and column cells. 
Describe the motor cells. 
These lie in groups in the anterior horn, an antero- 
median and postero-lateral, separate in the cervical and 
lumbar enlargements, but in the uppermost cervical 
and in the thoracic regions united in a single cluster. 
The cells possess a large cell body and long protoplas- 
mic processes, dendrites extending far into the sur- 
rounding substance. The nerve or axis cylinder pro- 
cess emerges from the summit of the anterior cornu, 
makes an oblique descent through the white substance, 
at the same time receiving a medullary sheath, and be- 
comes the axis cylinder of a medullated nerve fibre. 
Occasionally the axis cylinder process gives off a few 
lateral twigs before leaving the gray matter. It leaves 144 
GENERAL HISTOLOGY. 
the spinal cord as a part of the anterior root fibre bun- 
dle. All anterior root fibres arise from motor cells of 
the anterior horn and on the same, not opposite, side. 
Describe the column cells. 
These constitute the chief mass of the nerve cells of 
the gray substance, and lay partly scattered, partly 
grouped, in the lateral horn and dorsal nucleus. The 
majority are smaller than the motor nerve cells and 
possess fewer and less branched, but far reaching den- 
drites. 
How are the processes distributed ? 
The axis cylinder process, after sending out many 
collateral fibrils in the gray substance, enters the white 
substance; the anterior or lateral columns, rarely the 
posterior, either on the same or on the opposite side. 
What are commissure cells ? 
When the process enters the white substance on the 
opposite side, the cells are termed commissure cells be- 
cause the axis cylinder passes through the anterior 
gray commissure before entering the white substance. 
The commissure cells occupy an area embracing the 
central canal in an arch on the ventral side. 
Describe the “stem fibres.” 
After arriving in the white substance, the axis cylin- 
der process of the majority of the column cells divides 
into a vertical ascending and descending “stem fibre” 
which lies parallel to the longitudinal axis of the spinal 
cord and sends off twigs—collateral fibres—which re- 
turn to the gray substance, where they terminate in 
tufts of free fibrils; the stem fibres themselves finally 
terminate like the collateral fibres. CENTRAL NERVOUS SYSTEM. 
145 
How are the collateral fibres distributed? 
The collateral fibres that enter into the anterior col- 
umns are tolerably strong and penetrate the anterior 
cornua singly or in bundles, where they weave a net 
around the large motor cells. They are especially 
strong in the antero-lateral curve of the anterior horn. 
The collateral fibrils coming from the lateral columns 
which go chiefly to the substantia gelatinosa centralis 
and only those ventral to the substantia gelatinosa 
Rolandi are well developed; the latter pass to the op- 
posite side and form the dorsal or posterior commis- 
sure. 
How are the nerve processes of the column cells 
covered ? 
In the adult, they are enveloped in a medullary 
sheath. 
What direction do the processes take coming from 
Clark’s columsi? 
These do not divide in the white substance, but turn 
cranial ward and proceed to the cerebellum; and the 
axis cylinder processes of other column cells, when ar- 
rived in the white substance, turn without dividing 
either upward or downward. 
What are Deiter’s cells? 
Nerve cells of the first type, such as motor and 
column cells. 
What are interior cells? 
A cell whose nerve process rapidly divides, but re- 
mains in the gray substance; they occur in the poste- 
rior columns and are nerve cells of the second type. 
Where do the nerve fibres arise ? 
The fibres that enter the anterior and lateral columns 146 
GENERAL HISTOLOGY. 
arise in part from the medullated, collateral fibres and 
the ends of the nerve processes of the column cells; in 
part from the axis cylinder processes that come from 
the brain, such as the medullated fibres of the posterior 
roots which originate in the centripetal processes of 
the cells of the spinal ganglia. 
How do they enter the spinal cord ? 
The posterior root fibres enter the spinal cord in two 
groups; a lateral, which runs in the zona terminalis, and 
a median that runs in the posterior columns. The 
fibres do not enter the gray substance directly, but 
each first divides in Y shape into an ascending and de- 
scending “stem fibre,” from which numerous collateral 
fibres diverge at right angles and enter the gray sub- 
stance. 
How do the fibrils terminate ? 
After entering the gray substance, they distribute 
themselves with their tufts of terminal fibrils over 
nearly every point; one set, terminating mostly in the 
summit of the posterior horn, have their origin in the 
lateral root fibre group, and form a very fine fibred 
dense plexus, that lies partly in the substantia gelati- 
nosa Rolandi. The second set terminates in Clark’s 
column, and originates in the median root fibre group, 
as does a third set which passes through the middle of 
the substantia gelatinosa Rolandi ventralward into the 
anterior cornu, and there radiates fan-shape and sur- 
rounds the motor cells in a network of fibrils forming 
the reflex bundle. This and the collateral fibres of 
Clark’s column sink into the gray substance forming 
a curve with the concavity lateralward, and from a mass 
easily seen. CENTRAL NERVOUS SYSTEM. 
147 
How do the “stem fibres” terminate? 
After a long course they turn into the gray substance 
and end like the collateral fibrils in five branches. 
What is the white substance composed of ? 
Entirely of medullated nerve fibres, which are with- 
out the sheath of Schwann. They differ greatly in 
thickness. The majority nerve fibres run parallel with 
the long axis of the spinal cord. Sometimes the fibres 
take an oblique direction; these are especially numer- 
ous in front of the gray commissure, where they cross 
and form the white commissure. 
How is the supporting framework of the spinal cord 
constructed ? 
In two ways: 
I. Fibrous connective tissue extensions of the pia 
which penetrate the white substance as vessel sheaths, 
and grows thinner as it approaches the gray matter. 
2. The neuroglia, which consists mostly of nucleated 
elements, the glia cells, and possibly a small amount of 
homogeneous ground substance. 
How many kinds of glia cells are there ? 
Two—the ependymal cells and Deiter’s cells. 
Describe the ependymal cells. 
They line the lumen of the central canal in a single 
layer; when young they possess cilias. Their cylindri- 
cal bodies are prolonged in an extended process which 
in the foetus reaches the surface of the spinal cord and 
terminates in a simple or branched end. 
Describe Deiter’s cells. 
At first they lie in the gray substance, but later retire 148 
GENERAL HISTOLOGY. 
into the white substance and undergo many changes in 
shape. 
Describe the substantia gelatinosa Roiandi. 
In addition to the ganglion cells and nerve fibres 
traversing it, it is mostly a granular substance, a trans- 
formation of the numerous delicates processes of Dei- 
ter’s cells. 
THE BRAIN. 
What structures compose the brain? 
White and gray matter. 
How does the gray matter occur ? 
In four situations: 
I. Cerebral cortex, covering the outer surface of the 
hemispheres. 
2. Corpora striata, optic thaiaini, corpora quadn- 
gemina; all limited masses in the cerebral ganglia. 
3. Lining of the ventricles. 
4. Cerebellar cortex, covering the surface of the 
cerebellum. Other masses of gray matter also occur 
and have numerous connections with one another by 
means of fibre tracts. 
CEREBRUM. 
Into how many sections can the cerebral cortex be 
divided ? 
Into four zones, but not sharply differentiated. 
Describe the molecular layer. 
This is the most superficial, and in ordinary prepara- 
tions appears finely granular, and contains an inter- 
lacement of medullated fibres called tangential fibres 
from their horizontal position. CENTRAL NERVOUS SYSTEM, 
149 
What forms the reticulum ? 
Partly the dendrites of the pyramidal cells, and 
partly the processes of the glia cells. 
What are the cells of Cajal ? 
Irregularly shaped bodies found in the molecular 
zone, which have processes running parallel with the 
surface, from which lateral twigs ascend. Their func- 
tion is not determined. 
Describe the zone of the small pyramidal cells. 
This is characterized by ganglion cells of pyramidal 
form. The apex of the pyramid is prolonged into a 
long, ramifying protoplasmic process which sends out 
lateral twigs and enters the molecular zone, terminating 
in many branches. Smaller dendrites spring from the 
sides and inferior surface of the cell. 
How is the axis cylinder process disposed? 
This proceeds from the bas'e, and after giving off 
branched collateral fibres, passes as a rule to the white 
substance to become the axis cylinder of one, or by 
division, two nerve fibres. Sometimes it runs to the 
molecular layer and divides, entering the web formed 
by the tangential fibres. The nerve processes and the 
collateral fibres are enveloped in a medullary sheath. 
Describe the zone of large pyramidal cells. 
This is distinguished by the larger size of its cells. 
The large axis cylinder process, after sending several 
collateral fibrils into the gray substance, always goes to 
the white substance. 
Describe the layer of polymorphous nerve cells. 
Here the elements are mostly oval or polygonal; an 
apical dendrite is absent, but the nerve process, after 150 
GENERAL HISTOLOGY. 
sending off a number of lateral twigs, enters the white 
substance, where it passes into one or two nerve fibres. 
Where are second type ganglion cells found ? 
In the last three zones. The axis cylinder process is 
either confined to the gray matter in the vicinity of the 
cells, or extends to the molecular zone and terminates 
in many branches. 
How are the medullated fibres arranged? 
In the last two zones the thick, radiating bundles 
split up into single fibres near the zone of small pyra- 
midal cells. 
How are the radiating bundles formed? 
By the descending medullated nerve processes of the 
large and small pyramidal cells and by thick medul- 
lated nerve fibres of unknown source that ascend from 
the white substance toward the cortex, where they di- 
vide and subdivide into “super-radial” and the tan- 
gential interlacement, and finally end in branches. 
What are the stripes of Qermari or Baillarger? 
This name is given to a set of medullated collateral 
fibrils of the nerve processes of pyramidal cells which 
become condensed toward the super-radial reticulum. 
What is the inter=radial reticulum ? 
A name given to a set of medullated nerve fibres 
running transversely to the radiating bundles. 
What is the substantia reticularis alba? 
A modification of the cerebral cortex in the hippo- 
campal and uncinate convolutions, where the tangen- 
tial fibres are very numerous and form a net-like ex- 
tended white layer. CENTRAL NERVOUS SYSTEM. 
151 
CEREBRAL GANGLIA. 
What constitutes the cerebral ganglia? 
The gray substance consists of ganglion cells of vari- 
able size, medullated nerve fibres and neuroglia. 
GRAY SUBSTANCE OF VENTRICLES. 
How far does the ventricular gray substance extend? 
From the floor of the fourth ventricle, through the 
aqueduct of Sylvius into the third ventricle, to the tuber 
cenerum and the infundibulum. 
What is its composition? 
The gray substance of the ventricles is the origin of 
the cranial nerves, and is composed of neuroglia, nerve 
fibres and multipolar ganglion cells. In some locations 
the cells are distinguished by their size—nucleus of 
hypoglossal nerve—or by their peculiar form—spheri- 
cal ganglion cells in upper pair of the corpora quadri- 
gemina. 
CEREBELLUM. 
What layers compose the cerebellum ? 
From within outward, the granule layer, the layer of 
the cells of Purkinji—microscopic—and the molecular 
layer. 
Describe the granule layer. 
This is characterized by its rusty color and consists 
of numerous layers of small cells which exhibit a large 
nucleus and almost no protoplasm. 
Name the ganglion cells. 
Two kinds are found, both of second type, small and 
large granule cells. 152 
GENERAL HISTOLOGY. 
Describe the small ganglion cells. 
They are multipolar, with short protoplasmic pro- 
cesses and a delicate nerve process without medullary 
sheath which passes vertically into the molecular layer, 
where it divides into longitudinal T branches running 
parallel to the surface and terminating in free un- 
branched ends. These are the principal elements of 
the granule layer. 
Describe the large granule cells. 
These are less numerous, but are more than twice as 
large as the small granule cells, and of directly oppo- 
site distribution—the protoplasmic processes extend to 
the molecular layer and the nerve process divides and 
ends in a rich ramification penetrating within the 
granule layer. 
What nerve fibres are found in the granule layer ? 
Medullated nerve fibres partially fill the intervals be- 
tween the nerve cells. They are derived from the 
medullary tracts, and some end in the molecular zone. 
Describe the cells of Purkinji. 
These are large multipolar ganglion cells forming the 
middle stratum. The bodies are slightly pear-shaped 
and send two large protoplasmic processes into the 
molecular layer, where they ramify in planes transverse 
to the long axis of the convolution. 
From the opposite pole of the cell the axis cylinder 
process proceeds. This soon becomes medullated, and 
passing through the granule layer enters the white sub- 
stance of the cerebellum. Collateral fibrils are thrown 
out in the granule layer and some run back between 
the Purkinji cells. CENTRAL NERVOUS SYSTEM. 
153 
What cells compose the molecular layer? 
Large and small cortical cells, both multipolar gang- 
lion cells. 
Describe the large cortical cells. 
They lie in the lower half of the molecular layer and 
the protoplasmic processes extend mostly toward the 
surface. Their longer nerve process runs near the inner 
margin of the molecular layer transversely to the axis 
of the convolution, and sends toward the surface a few 
collateral fibres. In the deeper portions at intervals 
the terminal branches form a basket-like network 
around the bodies of Purkinji’s cells and often embrace 
also the beginning of the axis cylinder process. 
Describe the small cortical cells. 
These lie nearer to the surface, but the nerve process 
has been little investigated. 
Describe the neuroglia of the cerebellum. 
This consists of two kinds of cells; one of which, 
lying at the boundary of the granule layer, has a small 
body, and sends a few short processes inward and many 
long processes in a straight course to the surface, where 
they end in a triangular expansion, and form relatively 
thick peripheral glia layer. The others, stellate in form, 
resemble the mossy cells of the cerebral cortex and 
occur in all strata. 
How are the cerebellar elements united? 
contact; not by direct connection. 
Describe the white substance. 
Excepting the connective tissue, it consists of medul- 
lated nerve fibres without a neurilemma. 154 
GENERAL HISTOLOGY. 
What is the pituitary body composed of? 
A small posterior lobe and an anterior larger lobe. 
Describe the small posterior lobe. 
This really belongs to the brain and consists mostly 
of connective tissue, blood vessels and cells which 
closely resemble multipolar ganglion cells. 
Describe the anterior lobe. 
Derived as a diverticulum from the primary oral cav- 
ity, it contains tubular acini embedded in loose vascu- 
lar connective tissue, the majority of which are solid 
and filled with pale or dark cubical epithelial cells. A 
few of the acini are sometimes hollow and occasionally 
they contain celloid substance. 
Describe the pineal body. 
This is derived from a diverticulum of the primitive 
brain vesicle, and consists of epithelial cells, some of 
which have delicate processes and of connective tissue 
envelope, from which septa extend into the interior. 
What is the “brain sand?” 
Rounded concretions of variable size, with uneven 
surfaces, found in the interior of the pineal body. 
They are composed of an organic basis and calcium 
and magnesium phosphate. 
THE MEMBRANES. 
What tissues envelop the brain and cord? 
The dura mater and pia mater. 
Describe the dura of the spinal cord. 
It consists of compact connective tissue and numer- 
ous elastic fibres, flat connective tissue cells and plasma CENTRAL NERVOUS SYSTEM. 
155 
cells. The inner surface is covered with simple flat 
epithelial cells (endothelium). 
Describe the dura of the brain. 
This consists of two lamellae, an inner corresponding 
to the dura of the cord and like it in structure, and 
an outer corresponding to the periosteum of the verte- 
bral canal. Its component elements are like the inner 
lamellae except that the outer fibre bundles are ar- 
ranged transversely to the inner, and it is rich in blood 
vessels. 
Describe the pia mater. 
This is a two-layered sack. The outer, or arachnoid, 
is covered on its free surface with endothelium, and is 
not closely attached to the dura. The inner closely 
invests the surface of the brain and cord, and sends 
blood vessels into their substance. The arachnoid and 
the pia are joined by many trabeculae. 
What are the villi of the arachnoid? 
Evaginations of the arachnoid especially found near 
the superior longitudinal sinus, that push the attenu- 
ated dura before them into the venous sinus. The pia 
consists of delicate connective tissue bundles and plate- 
like cells which cover the inner surface. 
What are the telae choroidese and plexus thoroidese? 
These are vascular villous projections on the margin 
of a fold of the pia, that hang like a fringe within the 
ventricles; they are composed of connective tissue and 
blood vessels united into tufts or globules, and covered 
with simple cubical epithelium—ciliated in the new- 
born. 156 
GENERAL HISTOLOGY. 
Describe the blood vessels of the central nervous 
system. 
They form a narrow meshed capillary network in the 
gray and a wide meshed network in the white substance, 
and possess a so-called adventitial sheath. 
SUPRA RENAL BODY. 
Why is this organ described with the nervous sys= 
tem ? 
On account of its early history, the profusion of its 
nerve elements and the results of pathological processes. 
Name the constituent parts of the organ. 
The capsule, the cortex, and the medulla. 
Describe the capsule. 
It is composed of fibrous connective tissue of consid- 
erable thickness, and from this envelope many connec- 
tive tissue septa penetrate deeply into the soft cellular 
substance and break it up into cylindrical masses. 
Describe the cortex. 
This consists of aggregations of irregularly rounded 
or polygonal cells whose granular protoplasm some- 
times contains fat particles in addition to clear nuclei. 
How is the cortex divided? 
In three divisions, known as the zona glomerulosa, 
zona fasciculata, and zona reticularis. 
Describe the zona glomerulosa. 
This is characterized by the grouping of the cells 
into round or oval masses just beneath the capsule. 
Describe the zona fascicularis. 
Here the cells are grouped in cylindrical form. CENTRAL NERVOUS SYSTEM. 
157 
Describe the zona reticularis. 
Here the cells are scattered in irregular anastomos- 
ing cords and the cells are pigmented. 
Describe the medulla. 
The medulla contains granular and sometimes deeply 
pigmented polygonal cells arranged as cords and irreg- 
ular network in a framework of highly vascular con- 
nective tissue. 
Where are the ganglion cells? 
These occupy the medulla in great numbers, along 
with a rich network of non-medullated nerve fibres and 
conspicuous venous channels. 
Describe the blood vessels. 
They divide within the capsule and send many small 
twigs along the fibrous septa to form capillary networks 
around the cell groups of both cortex and medulla. 
The veins unite to form trunks passing out at the hilus. 
Describe the nerves. 
The nerves are remarkable both for number and size, 
and accompanying the arteries to the medulla, they 
there form an intricate plexus composed mostly of 
non-medullated fibres. DENTAL HISTOLOGY. 
Define dental histology. 
Dental histology is the study of the microscopic 
structure of the teeth and the tissues of the mouth. It 
is that part of general histology which treats of the tis- 
sues of special interest to the dentist; and it has to do 
not only with cells and their arrangement, but also with 
the results of cell life in formed material, such as den- 
tine and enamel. 
Of how many tissues are the teeth made up ? 
Four. 
Name the dental tissues. What part of the tooth is 
formed by each ? 
Enamel: covering the crown or exposed portion of 
the tooth. 
Cementum: covering the root portion of the tooth. 
Dentine: making up the mass of the tooth. 
Pulp; or soft tissue filling the central cavity in the 
dentine. 
From the standpoint of comparative anatomy, with 
what structures are the teeth analogous ? 
The dermal scales of such animals as the sharks and 
rays. 
Are the teeth a part of the osseous system ? 
No. 
159 160 
DENTAL HISTOLOGY. 
To what structures in the body are they allied ? 
To such structures as the nails and the hair. 
From the development, what is the analogy between 
the teeth and the hair? 
The tooth is developed from a papilla of connective 
tissue covered by an epithelial structure. The hair is 
an epithelial structure, supported on a connective tissue 
papilla. ENAMEL. 
How much organic matter is found in the enamel of 
the tooth ? 
Not more than 5 per cent. Dr. Williams’ recent 
work seems to show that in nortnal perfect enamel 
there is no organic matter whatever. 
What is the chemical composition of the enamel of 
the teeth ? 
(American System of Dentistry.) 
Water and organic matter 3.6 
Calcium phosphate and fluoride 86.9 
Magnesium phosphate 1.5 
Calcium carbonate 8.0 
What is the difference between the action of enamel, 
dentine and bone when treated with acid ? 
When treated with acid, bone and dentine have the 
inorganic salts dissolved out of them, and leave the or- 
ganic matter which retains the structure of the original 
tissue. When enamel is treated with acid no trace of 
structure is left. 
Compare enamel with other calcified tissues. 
Enamel differs from all other calcified tissues. Both 
bone and dentine are made up of a formed substance, 
which yields gelatine on boiling, and which was the 
result of cell activity, being analogous to the intercellu- 
lar substance of cartilage, into which the inorganic salts 
161 162 
DENTAL HISTOLOGY. 
have been deposited. When treated with acid this 
matrix of formed substance is left, maintaining the 
form of the tissue after all the salts have been removed. 
Enamel has no such matrix of organic matter in the 
adult tissue. Probably it normally contains no organic 
matter and never has more than 5 per cent. The matrix 
of formed substance, which gives the structure to the 
tissue in development, is perfectly transformed into 
inorganic matter in the adult tissue. 
Of what structural elements is the enamel made up? 
The enamel rods or prisms, sometimes called the 
enamel fibres; and the inter-prismatic or cementing 
substance, which is also perfectly calcified. 
Describe in a general way the enamel rods. 
The enamel rods are prismatic, usually five or six 
sided, and pointed at each end, passing out perpendic- 
ularly from the surface of the dentine. 
What is the diameter of an enamel rod ? 
Name the layers or portions of the enamel at the 
From 3.4 to 4.5 microns. 
time of eruption. 
The portion made up of the rods arranged parallel 
with each other, making the body of the enamel. 
The narceous layer of Sudduth. 
Nasmyth’s membrane. 
What is the narceous layer of Sudduth? 
The granular layer which covers the outer ends of 
the enamel rods giving to the outer surface of the tooth 
its smooth polished surface, is called by Dr. Sudduth 
the narceous layer, and is considered analogous to the 
similar layer in the shells of mollusks. ENAMEL. 
163 
What is Nasmyth’s membrane? 
Nasmyth’s membrane is the layer of horny scales 
which cover the crown of the tooth at the time of its 
eruption. Also called “the cuticula dentis.” 
What is Nasmyth’s membrane a remnant of? 
Nasmyth’s membrane is the remains of the inner 
tunic of the enamel organ. The columnar cells become 
flattened and horny and cover the tooth as a membrane 
at the time of eruption. The layer is very soon worn 
off. 
Describe the appearance of a section of enamel, cut 
across the rods. 
The section has very much the appearance of a tile 
floor. The cross sections of the rods appearing as 
irregular five- or six-sided areas separated by the 
cementing substance. 
Describe minutely the enamel rods and their rela= 
tion to each other. 
The enamel rods are long, usually five- or six-sided 
prisms pointed at both ends. Some of them pass from 
the surface to the dentine, but many others are shorter 
and end in points between the converging rods These 
rods are from 3.4 to 4.5 microns in diameter. They are 
not even in their outline, but present alternate expan- 
sions and contractions which are more marked in some 
specimens than in others. The rods lie parallel with 
each other, the enlargements in one rod lying opposite 
the enlargements in the ones next to it. The rods may 
be likened to rods of clay made by rolling up clay balls 
and pressing them together. In development the rods 
are formed in such a way, the sperules of calcoglobulin 
are formed in rows; these are surrounded with a cement- 164 
DENTAL HISTOLOGY. 
ing substance and both become perfectly calcified by 
substitution, organic matter being removed and inor- 
ganic substituted for it. 
What is meant by the striation of enamel ? 
The appearance of alternate light and dark bands 
similar in appearance to the striation of voluntary mus- 
cle. These striations appear even in low magnification 
and are caused by the variations in size of the rods. 
What is meant by the stratification of enamel? 
Stratification is the appearance, common to almost all 
enamel, of bands of brown or dark pigment. These bands 
are not parallel with the outline of the enamel, but are 
more curved; they mark lines of increment and are not 
caused by a difference in the form of the rods in that 
portion, but by a deposit of pigment with the lime salts 
in that part, and mark the rhythmic or intermittent for- 
mation of enamel. 
Describe the direction of the rods in different parts 
of the tooth. 
While the direction of the rods is outward, perpen- 
dicularly from the surface of the dentine, this is only a 
general statement; only in a few places are they straight 
and pass directly outward. The rods are more or less 
wavy in their course, and over the cusps are very much 
twisted and interwound. As you pass down the sides 
of the crown and approach the gingival margin, the 
enamel becomes very thin and the rods very short, and 
their direction is at more than a right angle to the axis 
of the tooth. 
What principles of operating are based on the direc= 
tions of the rods? 
The beveling of the margins of cavities, especially at ENAMEL. 
165 
the gingival margin. If the seat of the cavity is car- 
ried out at right angles to the axis of the tooth, the in- 
ner ends of the rods will be cut off and the outer ends 
left without support from the dentine; these unsup- 
ported ends are sure to be broken off in packing the 
filling, and leave a defective place. On the buccal and 
lingual margins of compound cavities in molars and 
bicuspids, the rods follow the direction of a radius and 
the enamel margins must be trimmed to this line so as 
to have the proper strength. 
When enamel is attacked by acids, what is first 
acted upon ? 
The inter-prismatic or cementing substance. This is 
seen when ground sections of enamel are treated with 
acid, as well as when the tooth is attacked by caries. DENTINE* 
By what other names is the dentine known ? 
The ivory. It is dentine that makes up the mass of 
the tusks of elephants and walruses, etc., and that den- 
tine is commercially known as ivory. 
Tooth bone. 
What cavity does the dentine inclose ? 
The dentine incloses a cavity in its center known as 
the pulp chamber. 
What fills this cavity in life ? 
The pulp or soft tissue containing blood vessels and 
nerves which nourish the tooth. It is commonly though 
incorrectly called the nerve. 
How do the blood vessels and nerves reach the pulp 
chamber? 
The blood vessels enter at the apical foramin, and 
pass down through the root canal occupying the cen- 
tral portion of the tissue in these fine canals. The 
canals are surrounded by dentine to the apical foramin, 
or very nearly, for a short distance at the end of the 
root the canalway passes through cementum, where the 
end of the root is made up only of cementum. 
What proportion of organic matter in dentine? 
Twenty-eight percent. 
What proportion of inorganic matter in dentine? 
Seventy-two per cent. 168 
DENTAL HISTOLOGY. 
What two kinds of organic matter in dentine ? 
The organic matrix, into which the salts are deposited 
and which gives the structure to the tissue, and the re- 
mains of the fibrils which fill the tubuli. Only that 
forming the matrix strictly belongs to the dentine. 
Give the chemical composition of the dentine* 
The following are two analyses given in the American 
System; 
Organic matter 27.61 20.42 
Fat 40 .54 
Phosphate and fluoride of calcium 66.72 67.54 
Carbonate of calcium 3-36 7-97 
Phosphate of magnesium 1.08 2.49 
Other salts 83 1.00 
Describe the effect of acids on the dentine. 
When the dentine is treated with acid, even very di- 
lute, the inorganic salts are dissolved out of the organic 
matrix, leaving the organic matter in the form that 
was characteristic of the calcified tissue. When treated 
in this way the entire tooth is attacked evenly, soften- 
ing the entire surface first and penetrating deeper and 
deeper till the entire tooth is decalcified. This action 
is to be contrasted with the decalcification of caries. 
What are the dentinal tubuli ? 
The dentinal tubuli are minute canals passing from 
the pulp chamber to the outer surface of the dentine, 
just under the enamel or ceraentum. 
What do they contain in life ? 
In life they are filled by the dentinal fibrils 
Give another name for the dentinal fibril. 
The fibres of Tomes. DENTINE. 
169 
From what do these fibres come? 
These fibres are prolongations from the odontoblasts. 
Do the dentinal fibrils penetrate between the en= 
amel rods? 
There is a difference of opinion on this point, but the 
best authority is that they do not. 
What is the diameter of the dentinal tubule? 
From 1.1 to 2.3 microns. 
Describe in detail the structure of the dentinal tu= 
bule. 
The dentinal tubuli pass outward from the pulp 
chamber to the outer surface of the dentine, just be- 
neath the cementum or enamel. In the crown portion 
their course presents a characteristic “ f” or “s” shaped 
curve, so that the tubule opens from the pulp chamber 
at right angles to the surface of the dentine and ends 
under the enamel at right angles to the line of union. 
In passing outward from the pulp chamber the 
tubule at first presents few or no branches, but in the 
outer portion the branches become very numerous, ap- 
pearing as little rootlets given off at an acute angle 
and anastomosing very freely with each other. Just 
under the enamel or the cementum they end in enlarge- 
ments which are often at right angles to the course of 
the tubule. 
What is the sheath of Neumann? 
The sheath of Neumann is a layer of partially calci- 
fied matrix surrounding the dentinal fibril, and lining 
the dentinal tubule. They are the most indestructible 
part of the dentine, resisting the action of acids and 
subsequent prolonged boiling in strong alkalies. Their 
exact nature is a matter of dispute. 170 
DENTAL HISTOLOGY. 
What is the granular layer of Tomes? 
The granular layer of Tomes is the layer of dentine 
just beneath the enamel or cementum. As the name 
indicates, it is granular in appearance, showing round 
or irregular spaces. 
What causes the appearance? 
The dental tubuli end in bulbous or irregular en- 
largements which are filled with living protoplasm, and 
which cause the granular appearance of the layer of 
dentine just beneath the enamel and cementum, known 
as the granular layer of Tomes, 
Where do the tubuli branch most freely? 
In the root portion of the tooth and in the outer por- 
tion of their course. 
What are the two kinds of curves in the dentinal 
tubule? 
The tubule presents two distinct curves in its course, 
a double curve in the general direction of the tubule so 
that at its opening into the pulp chamber it is about 
perpendicular to the inner surface of the dentine, and 
at its outer end it is about perpendicular to the line of 
union between the enamel and dentine. Besides this 
curve in its general direction the tubule presents a 
great many wavy curves throughout its course which 
do not affect its general direction; as many as 200 of 
these wavy curves have been counted in the length of 
a single tubule. 
Do the tubuli communicate with the canaliculi of 
the cementum ? 
There is more or less difference of opinion on this 
point, but they probably do. DENTINE. 
171 
What are the incremental lines of Salter? 
The incremental lines of Salter are lines appearing 
in sections of dried teeth. They run in a direction par- 
allel with the line between the enamel and the dentine, 
and are probably caused by the shrinkage of the tooth 
in drying. 
What are the inter=globu!ar spaces ? 
The inter-globular spaces are portions of the dentine 
where the matrix has not been calcified, thus leaving 
irregular shaped spaces, filled only with organic matter. 
They are not empty spaces, but are points of imperfect 
development. Sometimes they are very extensive. 
What are they filled with? 
With uncalcified matrix of the dentine. The tubuli 
pass through them. 
Is dentine formed after the tooth is erupted? 
Yes. The formation of dentine goes on normally 
through life, consequently the pulp chamber in young 
teeth is larger than in old ones. The formation of 
secondary dentine may be caused by any irritation act- 
ing on the pulp, as advancing decay, exposure to heat 
or cold, etc., etc. 
What is the characteristic of secondary dentine ? 
The structure is less perfect. The tubuli are always 
crooked and irregular, and not like the tubuli of the 
body of the tooth. 
Is dentine ever reformed after absorption ? 
No. 
When dentine on the surface of a root is removed 
by absorption, how is the breach refilled ? 
the formation of cementum. CEMENTUM. 
Where is the cementum found? 
Covering the surface of the roots of the teeth. 
What is the cementum sometimes called, especially 
in the older books and in medical books ? 
“Crusta Petrosa.” 
What tissue of the body does it resemble ? 
Bone. 
What is the difference between bone and cementum ? 
Cementum contains no Haversian canals. 
Do you ever find Haversian canals in cementum ? 
No. 
Is there a difference of opinion on this point? 
Yes. 
What is probably the true nature of what some ob- 
servers have called Haversian canals in the ce= 
mentum ? 
They are places where blood vessels have been em- 
bedded in the cementum, forming a canal around them, 
but these canals have no concentric arrangement of the 
lamellae of cementum around them, such as is neces- 
sary for the formation of a Haversian system in bone. 
These canals are simply foramina. Instead of having 
an apical foramen simply, the tooth has one or more 
foramina on the side of the root. 
173 174 
DENTAL HISTOLOGY. 
These lateral foramina are probably formed in this 
way. When the dentine is being formed the dental 
papilla is a cone-shaped structure, the blood vessels 
entering at the base. As the dentine is formed the 
papilla is covered in more and more and the blood 
vessels which entered at the base from all directions 
are cut off, leaving only those at the center to supply 
the pulp. Sometimes one of the vessels, instead of be- 
ing cut off or deflected, persists and is embedded in the 
dentine, and later when the dentine is covered with 
cementum the vessel is inclosed in it. 
Describe the structure of the cementum. 
The cementum is very thin at the neck of the tooth, 
where it slightly overlaps the enamel; passing down 
the root it becomes thicker and thicker, often form- 
ing quite a portion of the end of the root. It is 
formed in regular layers one upon the other, like the 
lamellae of bone. Between these layers are found small 
spaces or lacunae, like the lacunae of bone, in which 
the cement corpuscles are found These spaces com- 
municate with each other by minute canals, the canalic- 
uli, which also probably communicate with the den- 
tinal tubuli. In the thin portion of the cementum near 
the neck of the tooth the lacunae and also the canalic- 
uli are scarce or entirely absent, but in the thicker 
portions, around the apex and at the bifurcation of the 
roots of molars, they are very numerous. 
The cementum is filled with the fibres of the peri- 
dental membrane which have been embedded in it and 
then calcified. The size and number of these fibres 
vary in different animals. 
What is the function of the cementum ? 
The function of the cementum is to furnish the at- CEMENTUM. 
175 
tachment for the fibres of the peridental membrane. 
Do you ever have a root without any cementum ? 
No. 
In what portion of the cementum are the lacunas 
most numerous? 
In the thick portions, at the apex of the root and be- 
tween the bifurcations of roots. 
Where are they usually absent or scanty ? 
Along the sides of the roots toward the neck of the 
tooth where the cementum is thin. 
Does the observation of the cementum give any judg= 
ment as to the age of the tooth ? 
An observation of the cementum can give only a 
general idea of the age of the tooth, that is, the length 
of time the tooth has been erupted, but it may give a 
very accurate idea as to relative times in the tooth’s 
life history. For instance, if absorption has occurred 
on the root at one time and hypertrifies at another, you 
are able to tell which occurred first and something 
about the time between the two. 
Upon what fact is the judgment based? 
The cementum is formed in successive layers, so that 
the layers record the growth of the tissue in the same 
way as the rings in the wood of a tree record the growth 
of the tree, A single layer is not necessarily continu- 
ous all over the surface of the tooth, but in any given 
area a layer which lies above has been formed more 
recently than any layer which lies beneath it. 
How do absorptions on the surface of the root leave 
a permanent record in the tissue? 
The cavity formed by the absorption is not filled by 176 
DENTAL HISTOLOGY. 
a local formation of cementum confined to the depres- 
sion, but the next layer of cementum which is formed 
over the surface of the root dips down into the concav- 
ity made by the absorption, and is thicker in that por- 
tion so that by the time several layers have been formed 
the concavity is obliterated. 
How are the fibres of the peridental membrane at= 
tached to the tooth ? 
The cementum is built up around them and they are 
calcified with the cementum matrix. 
What other structure in the body do they resemble ? 
Sharpey’s fibres in the attached portions of the 
periosteum. 
By what is the surface of the cementum covered? 
The entire surface of the cementum is normally cov- 
ered by the peridental membrane. When the cementum 
is uncovered it is by an abnormal recession of the peri- 
dental membrane and gum. 
What is exostosis? 
Exostosis is the formation of an excessive amount of 
cementum on the root of a tooth. The formation may 
be confined to a small area or may involve almost the 
entire root. The hypertrify is usually caused by a 
thickening of each of the layers of cementum in that 
portion of the tissue, but there may be as well a greater 
number of layers in that portion. PULP 
Where is the pulp found ? 
Filling the cavity of the dentine. 
What is it commonly though improperly called? 
The nerve. 
Of what kind of tissue is the pulp made up? 
The pulp is chiefly made up of embryonal connective 
tissue richly supplied with blood vessels and nerves. 
What is the characteristic of an embryonal connec= 
tive tissue ? 
An embryonal connective tissue is one in which the 
cells are widely scattered in a gelatinous intercellular 
substance. As a rule, the cells are embryonal in char- 
acter in that they are capable, under special conditions, 
of undergoing special development. 
Name the four kinds of cells found in the pulp- 
Spindle cells 
Round cells. 
Stellate cells 
Odontoblasts 
Name the three portions of the pulp in reference to 
the arrangement of the cells. 
The outer surface of the pulp, next to the dentine, is 
covered by the layer of the odontoblasts. 
177 178 
DENTAL HISTOLOGY. 
Just beneath the odontoblasts is a layer in which the 
cells are very few and widely scattered. 
Just beyond this layer the cells are rather more nu- 
merous than in the body of the pulp. 
And the body of the pulp in which the cells are 
scattered through the matrix. 
Describe the cells of the pulp. 
In thin section the cells are seen widely separated. 
Most of the cells are stellate or spindle shaped. Each 
cell has a round nucleus about which is a small amount 
of protoplasm which is prolonged out into the inter- 
cellular substance in fine filaments that are not always 
well seen. The round cells are more numerous in some 
sections than in others, and it is not always possible to 
tell whether the cell is spherical or whether the round 
outline is simply due to cutting a spindle cell across at 
right angles to its long axis. 
If the section is thick the cells seem to be close to- 
gether, but that is because they lie one above the 
other. 
Where are the odontoblasts found? 
The odontoblasts are found covering the outer sur- 
face of the pulp next to the dentine. 
What is the “flembrana Eboris?” 
The membrana eboris is the name given to the layer 
of odontoblasts by the older writers. 
Describe an odontoblast. 
The odontoblasts are flask-shaped or club-shaped 
cells, each with a large oval nucleus. The cells form a 
single or a double layer on the outer surface of the 
pulp. The nucleus is found in the enlarged end of the 
cell away from the dentine; the other end of the cell is PULP. 
179 
prolonged into a long protoplasmic process which 
passes into the dentinal tubule and is called the fibre of 
Tomes or the dentinal fibril. It penetrates the entire 
thickness of the dentine, and ends next the enamel or 
cementum in an enlargement in the granular layer of 
Tomes. In some cases two fibrils can be traced from 
one cell into two tubuli. The odontoblasts lie very 
close together, with little or no intercellular substance 
between them. The fibres branch and divide in their 
course as the dentinal tubuli do, and these branches 
communicate with each other very freely in the outer 
part of their course, putting one odontoblast in com- 
munication with a considerable area of the dentine on 
the outer surface. 
What is the function of the odontoblasts ? 
The formation of dentine. 
What embryonal structure is the pulp a remnant of ? 
The dental papilla. 
What are the functions of the pulp? 
The pulp has a sensory function and a vital function. 
The sensory function is the recognition of tempera- 
ture or rather of changes of temperature and of other 
causes of irritation. This is peculiar to the pulp; it is 
not shown by the peridental membrane. 
The vital function is the formation of dentine. 
What differential diagnosis is based on the sensory 
function of the pulp? 
The differentiation between a tooth with a live pulp 
and a tooth with a dead one. If the pulp is dead and 
the tooth be touched with cold water or with a hot in- 
strument no sensation will be experienced, but if the 180 
DENTAL HISTOLOGY. 
pulp is alive it will manifest it by a sharp twinge of 
pain. 
The recognition of the cause and initial locality of 
an alveolar abscess can sometimes be accomplished only 
in this way. 
Is the pulp a specially vascular tissue ? 
Yes. 
What is the characteristic of the blood vessel walls ? 
All the blood vessels of the pulp have very thin walls. 
The arteries have usually only a single layer of muscle 
fibres, and many of the veins, even of considerable 
size, have but a single layer of endothelial cells in their 
walls. 
Describe the blood supply of the pulp. 
One artery, sometimes two or three, enter the pulp 
at the apical foramen; they pass down the center giv- 
ing off lateral branches which pass out to the periphery 
of the pulp, where they break up into a very rich capil- 
lary plexus beneath the odontoblasts. From this 
plexus the blood is collected in the veins which pass 
up through the central portion and one or more leave 
the pulp through the apical foramen. An injected 
specimen shows the vessels very well, the small veins 
and capillaries making a fine network throughout the 
tissue, and the large vessels with more direct course 
occupying the central portion of the organ. 
To what pathological condition does the structure 
of the blood vessel walls make the pulp specially 
liable ? 
The thinness of the blood vessel walls, and the fact 
that they lie in a tissue largely made up of gelatinous PULP. 
181 
intercellular substance, makes the pulp specially liable 
to hyperaemia and inflammation. 
Describe the condition and the consequent effects. 
A chemical irritant acting through a carious cavity 
or sudden thermal changes affect the muscular wall of 
the arteries causing them to relax, thus allowing more 
blood to enter the organ and over-filling the veins and 
capillaries with blood. This may be simply a passing 
flush, as when something cold is brought against a 
tooth in eating, causing a sudden twinge of pain which 
passes off at once, or if the irritant is constant in its 
action the condition is maintained. 
If a tooth is extracted in a paroxysm of hyperaemia 
and examined under the microscope, if it is simply a 
passing flush the blood vessels are found large, dis- 
tended and filled with blood; but if the pulp has been 
in that condition for some time, many of the blood ves- 
sels will be found to show a pouching of the walls or a 
varicose condition. 
A hyperaemia of the pulp usually passes on to inflam- 
mation or returns to the normal condition. In rare 
cases there may be death of the pulp and complete 
infarction following a very acute hyperaemia in this 
way; the attack is very acute, the relaxation of the 
arteries is so complete and the arterial pressure so high 
as to compress the veins at the apical foramen, and 
check the escape of the blood from the pulp The 
circulation is stopped and the pressure ruptures the thin 
walls of the vessels and a hemorrhagic infarct results. 
When suppuration occurs, what course does it fol= 
low? 
When suppuration occurs it follows the course of the 
large veins passing down the center of the pulp. 182 
DENTAL HISTOLOGY. 
What is the general course of the nerves in the 
pulp ? 
One medullated nerve fibre enters the pulp at the 
apical foramen and its branches follow, in general, the 
course of the blood vessels. 
Where is the terminal plexus found? 
The terminal plexus of nerves is found in the clear 
layer just beneath the layer of odontoblasts. 
Have nerves ever been demonstrated penetrating the 
dentinal tubuli ? 
No. 
To what degenerative changes is the pulp specially 
liable ? 
Calcification and deposits of calcoglobulin. PERIDENTAL MEMBRANE 
What is the peridental membrane? 
The peridental membrane comprises that tissue which 
intervenes between the root of the tooth and the bony 
wall of the alveolus. 
By what other names is it known ? 
Alveolo-dental periosteum, or pericementum, 
Give one reason why it may be considered the most 
important of the dental tissues. 
The usefulness of the tooth depends upon the health 
of the peridental membrane. Though the tooth be 
perfect in every other respect, if the peridental mem- 
brane is in an abnormal condition it will not tolerate 
use in mastication, for the inflamed membrane will not 
bear the force brought against it. 
What are the three functions of the membrane, and 
define each? 
A physical function; to hold the tooth in its position 
in the jaw. 
A vital function; the formation of cementum. 
A sensory function; the sense of touch, as distin- 
guished from temperature sense. 
Why is it not proper to call the membrane “peri= 
osteum ?” 
“The membrane not only fills the space between the 
tooth and the alveolar wall, but surrounds the tooth 
183 184 
DENTAL HISTOLOGY 
above the margin of the alveolus and supports the gum 
about the neck of the tooth. The fibres of the mem- 
brane are larger, stronger and more numerous than 
those of the periosteum in any of its attached portions. 
The tissue contains structures of a glandular nature 
never found in the periosteum, and its functions are 
not analogous to those of the periosteum in any posi- 
tion.” 
What are the structural elements of the membrane? 
Fibres. 
Fibroblasts. 
Cementoblasts 
Osteoblasts. 
Osteoclasts. 
Glands. 
To which is the physical function due? 
The fibres. 
What kinds of fibrous tissue do you find in the 
membrane ? 
The mass of the membrane is made up of white 
fibrous tissue. The tissue is divided into two classes— 
I. The principal fibres. Those which spring from the 
cementum of the root and are attached to the bone of 
the alveolus or the surrounding tissue, thus performing 
the physical function of holding the tooth in its alve- 
olus. 2. The indifferent or inter-fibrous tissue. The 
tissue made up of fibres and cells which fill the spaces 
between the principal fibres and surround and accom- 
pany the blood vessels and nerves. 
Is there any elastic tissue in the membrane? 
No. When the white fibres are dissolved by reagents, 
no elastic fibres are left as in tissues containing both. PERIDENTAL MEMBRANE. 
185 
Define the principal fibres. 
Principal fibres is the name Dr. Black has given to 
the. large fibres of the membrane which are attached at 
one end to the cementum and at the other to the bone 
of the alveolus or the tissue of the gum. They are 
made up of fasciculi of smaller fibres. The fasciculi 
break up into their component small fibres in the cen- 
tral portion of the membrane, and are reunited to be 
attached to the bone so that the fibres are continuous 
from tooth to bone. 
Define the indifferent fibrous tissue. 
The indifferent fibrous tissue is made up of small 
fibres accompanied by fibroblasts. These fibres, fill the 
spaces between the principal fibres, and in these places 
the direction of the fibres is often different from that 
of the principal fibres. About the blood vessels and 
nerves the indifferent fibrous tissue is arranged in a 
concentric way, surrounding and accompanying the 
vessels and nerves. 
Into what parts is the membrane divided for study 
and reference? 
1. Gingival, 2. Alveolar. 3. Apical. 
1. The gingival portion surrounds the neck of the 
tooth below the border of the alveolus and supports 
the gingivus. 
2. The alveolar portion is that between the border of 
the alveolus and the apex of the root. 
3. The apical portion of the membrane surrounds the 
apex of the root. 
Describe the arrangement of the principal fibres in 
the gingival portion of the membrane. 
On the labial and lingual sides of the root the fibres 186 
DENTAL HISTOLOGY. 
spring from the cementum in large bundles and pass 
out, breaking up somewhat into smaller fibres and are 
lost in their attachment to the fibrous mat of the 
gum. Toward the mesial and distal sides the fibres 
bend around laterally and pass directly from tooth to 
tooth. They spring from the cementum of one tooth 
as large fibres, break up into smaller fibres which are 
deflected from their direct course to pass around fibres 
which are parallel with the axis of the tooth, and are 
finally reunited into large fibres and attached to the 
cementum of the adjoining tooth. 
Describe the arrangement of the fibres in the alve- 
olar portion of the membrane. 
In the alveolar portion of the membrane the fibres 
pass from the cementum to the bone of the alveolar 
wall. In the lower part (near the gingival border) the 
fibres are large and do not break up into smaller fibres 
as much, in passing across to the bone, as in most 
parts of the membrane; in many cases you are able to 
follow an individual fibre from the cementum to the 
bone without losing its identity at all. 
In the lower part of the alveolar portion just at its 
border the fibres pass obliquely from the cementum to 
the bone, being inclined toward the apex of the root. 
Just beyond the border of the alveolus, and for a short 
distance along the root, the fibres pass directly from 
the cementum at right angles to the axis of the tooth. 
In this position the single fibres are larger, and more 
often pass from the cementum to the bone without 
dividing than in any other part of the membrane. 
Farther toward the apex the fibres again become 
oblique, but they are inclined in the opposite direction, 
and the inclination increases more and more toward 
the apex. In passing from the cementum to the bone PERIDENTAL MEMBRANE. 
187 
the fibres run toward the margin of the alveolus, away 
from the apex of the root. 
Many of the fibres springing from the cementum 
near the apex are large, and as they pass out across 
the membrane break up into fan-shaped fasciculi to be 
attached to the wall of the alveolus. 
Describe the arrangement of the principal fibres in 
the apical portion of the membrane. 
In the apical portion the principal fibres are large 
and break up into fan-shaped fasciculi, which spread 
out in all directions to be attached to the bone. The 
spaces between the fibres are large and are occupied in 
the young largely by embryonal tissue; the amount of 
indifferent fibrous tissue increases as age advances. 
In the young, the tissue in this portion resembles 
that of the pulp or the dental papilla. 
What is the dental ligament ? 
In the gingival portion of the membrane many fibres 
springing from the cementum pass out, first decussat- 
ing with, then blending with fibres springing from the 
bone and bend down into the gingivus, thus forming a 
strong band of fibres which support the gingivus and 
hold it against the neck of the tooth. 
Discuss the arrangement of the principal fibres with 
reference to the physical function of the mem= 
brane. 
The arrangement of the principal fibres is the best 
that could be devised for holding the tooth in its posi- 
tion in the jaw. At the alveolar margin the fibres are 
inclined toward the apex of the root holding the tooth 
into the alveolus. Just below the margin of the alve- 
olus the fibres are specially large and pass out at right 
angles to the axis of the tooth, supporting it against 188 
DENTAL HISTOLOGY. 
the lateral strain of mastication. Farther down in the 
alveolar portion the fibres are arranged so as to swing 
the tooth in its socket, supporting it against the force 
of occlusion. 
What are the cellular elements of the membrane? 
Fibroblasts. 
Osteoblasts. 
Osteoclasts. 
Cementoblasts. 
Glands. 
Describe the fibroblasts and their arrangement. 
The fibroblasts are spindle shaped cells which lie be- 
tween the fibres and accompany them. They are much 
more numerous in the young than in the old. 
Describe the osteoblasts of the membrane. 
The osteoblasts of the membrane are exactly like 
those of the periosteum in its attached portions. They 
are cuboidal cells with granular protoplasm and a large 
round nucleus. They lie between the fibres on the 
surface of the bone, with the formation of which they 
are immediately concerned. They present fine proto- 
plasmic processes extending into the matrix of the 
bone. 
What are the osteoclasts ? 
Osteoclasts are large or giant cells with many nuclei 
which have the power of dissolving calcified tissue. 
Describe an osteoclast and contrast it with an oste= 
oblast. 
The osteoclasts are large, two or three times as large 
as an osteoblast; they always have several nuclei and 
are found lying in depressions which they have scooped PERIDENTAL MEMBRANE. 
189 
for themselves in the surface of the bone or cementum 
with which they lie in contact. 
By what other name are the osteoclasts in the peri- 
dental membrane sometimes called? 
Cementoclasts, 
Why does the word seem unnecessary? 
The cells are morphologically the same. There is no 
difference in appearance or structure between what are 
called osteoclasts and cementoclasts, and their origin 
is probably the same; in one case the cell is acting on 
bone, in the other it is acting on cementum. Osteo- 
clasts may be defined as cells which destroy calcified 
tissue of any kind; the word cementoclast defines them 
in reference to their location; that is, a cementoclast is 
an osteoclast which is destroying cementum. 
What are the cementoblasts ? 
Cementoblasts are cells which form cementum. 
Describe a single cementoblast. 
The cementoblasts are flattened in form, and never 
resemble the osteoblasts, which are always cuboidal. 
They cover the entire surface of the root between the 
fibres, and their outline is notched so as to fit in between 
and around the fibres. Each cell is made up of granu- 
lar protoplasm, with a single large, round or oval 
nucleus. Protoplasmic processes penetrating the cemen- 
tum have not been demonstrated, though it is probable 
that they exist. 
Describe the formation of the cementum by the 
cementoblasts. 
The cementoblasts cover the entire surface of the 
root. They form the matrix in regular lamellae and 190 
DENTAL HISTOLOGY. 
then superintend the deposit of lime salts into the 
matrix. 
Occasionally one of the cementoblasts is embedded 
in the formed matrix and becomes one of the cement 
corpuscles. The cementoblasts cover the surface 
of the root, lying between the fibres; as they build up 
cementum, they include the fibres in the formed cemen- 
tum and the salts are deposited in the fibres as well as 
the matrix. In this way the fibres are firmly fastened 
to the tooth. 
Describe the absorptions which occur in the cement= 
uni. 
When an absorption occurs in the cementum the 
first thing which happens is the cutting off of the fibres 
at that point by the osteoclasts; they then attack the 
cementum, scooping out a hollow in it in which they 
lie close against the surface attacked. The surface is 
not softened to any depth, but if the osteoclasts are 
removed from an absorption surface it is found to be 
smooth and polished. It is necessary for the cells to 
be in absolute contact with the surface destroyed. 
What may be the cause of an absorption ? 
Absorptions are very often found on the root and 
are probably due to many causes, some of which are 
very obscure. At about the time the tooth reaches full 
occlusion they are almost always found and are proba- 
bly caused by the movements necessary to bring the 
cusps into full occlusion with the opposing tooth. 
After an absorption, how is the contour of the tooth 
restored ? 
After the absorption has ceased the next layer of 
cementum to be formed over the surface of the root PERIDENTAL MEMBRANE. 
191 
dips down into the cavity formed, and in that portion 
the layer is thicker than on the rest of the root surface, 
so that after a few layers have been formed the con- 
tour of the root is restored. 
How are the movements of the tooth, either natural 
or artificial, accomplished ? 
The movements of the tooth and alveolus, such as 
are necessary in the correction of irregularities of the 
teeth, are accomplished by a combined or co-ordinated 
action of the osteoblasts and osteoclasts. The osteo- 
clasts cut off the attachments of the fibres and remove 
the bone of the alveolar wall in the direction of the 
pressure which is put on the tooth; then the osteo- 
blasts build in new bone, forming a new alveolus and 
reattaching the fibres so that the tooth becomes solid 
again. The fibres are never all cut off at one time; 
while they are being cut off at one point and the bone 
absorbed, they are being attached at another by bone 
being built around them. 
The natural movements of the tooth in development 
from childhood to maturity are accomplished in the 
same manner. 
Describe the movements of the anterior superior 
teeth in the development from childhood to ma- 
turity. 
After eruption is complete the entire tooth and 
alveolus is moved downward and forward with the de- 
velopment of the bones of the face, causing the length- 
ening of the face characteristic of this period. The 
movement is accomplished by the same means as the 
artificial movements in regulating. Bone is built up 
around the margin of the alveolus and the alveolus is 
filled up from the bottom, increasing the height of 192 
DENTAL HISTOLOGY. 
the alveolar process. In the same time the distance 
between the tooth and the bone of the alveolus which 
was great at the time of eruption, to allow the passage 
of the crown of the tooth, is reduced by the formation 
of bone all around the wall of the alveolus. 
Where are the glands of the membrane found ? 
The glands of the membrane are found between the 
fibres close to the cementum. 
Describe the arrangement of these structures. 
The glands form a network around the root extend- 
ing almost to the apex. This network is quite close in 
the gingival portion and becomes more open as you 
approach the apex. As many as 200 have been 
counted in a cross section of a central incisor, through 
the-gingival portion. 
Describe the cells of these structures. 
The cells are epithelial in character with granular 
protoplasm, which takes the stain strongly; each has a 
large distinct nucleus. They are- arranged in threads 
like tubular glands. In cross sections they show five 
or six or more cells, arranged in a circle or whorl, and 
they are inclosed in a very delicate membrane. The 
threads are not straight, but wind in and out between 
the fibres, giving an appearance similar to that of a 
tubular gland. No lumen or duct has ever been dem- 
onstrated. 
Describe the blood supply of the peridental mem 
brane. 
Four or five blood vessels enter the membrane at the 
apical space and pass downward, supplying the tissue 
with a fairly rich capillary plexus. As these vessels 
pass down through the membrane they receive lateral PERIDENTAL MEMBRANE. 
193 
branches which enter the membrane through the Ha- 
versian canals which open on the sides of the alveolus. 
These lateral branches are sufficient to maintain the 
size of the vessels, in spite of the capillary plexus 
which they supply. At the gingival border they re- 
ceive branches which enter over the margin of the 
alveolus. There is, therefore, a double or triple 
source for the blood supply of the membrane. Vessels 
entering at the apical space, at the margin of the alveo- 
lus and through the Haversian canals in the sides of the 
alveolus. 
What is the importance of this arrangement of the 
blood supply? 
When the vessels entering at the apical space are 
obliterated by suppuration involving that portion of 
the membrane, the nourishment of the entire membrane 
is not cut off, but the gingival and alveolar portions are 
supplied by the vessels which enter through the Haver- 
sian canals in the sides of the alveolus and over the 
margin. 
What disease probably originates in the glands of 
the membrane ? 
Phagedenic pericementitis, which first shows a de- 
generation and finally a suppuration of the glands, 
resulting in destruction of the membrane. 
Describe the changes in the membrane with advanc= 
ing age. 
The thickness of the membrane decreases as age ad- 
vances by the formation of bone on the inside of the 
alveolus and the formation of cementum on the surface 
of the root. The number of cellular elements de- 
creases, the glands become somewhat fewer in number. 194 
DENTAL HISTOLOGY 
In the young membrane the blood vessels are found in 
the center, half way between the cementum and the 
bone, and form quite a vascular area there; in the older 
membrane the blood vessels come to lie close to the 
bone, often in grooves in the wall of the alveolus. EMBRYOLOGY 
Define embryology. 
Embryology is the study of the development of the 
individual from the fertilized ovum or egg. 
From the standpoint of evolution, what relation is 
there between the development of the individual 
and the development of the race or type ? 
The higher animals pass through in a few months or 
weeks the development from an animal of one cell to 
the fully developed type; made up of many tissues 
with special functions, made up of millions of cells, 
and with the organs especially adapted to their use. In 
this development the individual passes through many 
stages corresponding to types which the race has 
passed through in its development from the lower 
forms of life. But these stages are hurried over, as if 
the race development of many centuries were condensed 
into a few months in each individual. 
What is the ovum ? 
The ovum is the cell produced by the female, which, 
when combined with the male element, has the power 
of reproducing the type 
What is the difference between the animals classed 
as oviporous and those classed as viviporus? 
Viviporus animals bring forth their young alive. The 
oviporus animals lay eggs which hatch outside the 
195 196 
DENTAL HISTOLOGY. 
body. Only the early stages of division of the ovum 
are accomplished in the body of the parent, then the 
ovum with a small amount of nourishment is discharged 
to complete its development outside of the parent. 
In the viviporous animals there is an ovum just the 
same, but if fertilized it is retained within the body of 
the parent and is nourished by the parent till develop- 
ment to the type is completed or is almost completed, 
when the young is brought forth alive. 
What is the sperm ? 
The sperm is the male element which unites with the 
ovum to reproduce the individual. 
What is fecundation ? 
Fecundation is the union of the sperm with the 
ovum. More accurately, it is the union of the head of 
the sperm with the nucleus of the ovum producing the 
segmentation nucleus. 
What is maturation ? 
Maturation is a process by which the fecundated 
ovum divides with karyokinetic figures forming two 
bodies, the polar bodies, which are cast off before seg- 
mentation begins. The exact significance of the pro- 
cess is not known, but has been the subject of much 
speculation. 
What is segmentation ? 
Segmentation is the process of division of the fecun- 
dated and maturated ovum, first into two, then four, 
then eight cells and so on till a hollow sphere is 
formed, the center of which is known as the segmenta- 
tion cavity. 
What is the gastrula ? 
The gastrula is formed from the segmentation sphere EMBRYOLOGY. 
197 
by a process of invagination forming a double layered 
bag. This corresponds to the type of such animals as 
the hydra and coral. 
What are the layers of the blastoderm ? 
Epiblast, 
Mesoblast. 
Hypoblast. 
Where is the epiblast found? 
The epiblast makes up the outer layer of the gas- 
trula or blastoderm. 
Where is the hypoblast found? 
The hypoblast is the inner layer of the gastrula lining 
the cavity of the double bag, or the deepest layer of 
the blastoderm. 
Where is the mesoblast found? 
The mesoblast is found between the epiblast and the 
hypoblast. In the gastrula it first appears where the 
epiblast and hypoblast join around the opening where 
the invagination took place. 
What is the difference between the epiblast, meso= 
blast and hypoblast, and the epiderm, mesoderm 
and hypoderm? 
The termination “blast” refers to the layers of the 
blastoderm or gastrula. From these layers the three 
characteristic embryonal tissues, the epiderm, meso- 
derm and hypoderm, are formed, and from these all the 
tissues of the adult organism. 
What tissues in the body are developed from the 
epiderm ? 
From the epiderm the entire nervous system is de- 
veloped, the epithelium covering the surface of the 198 
DENTAL HISTOLOGY. 
body, the enamel, the nails, the hair, the organs of 
special sense, and all glands except those opening on 
the alimentary canal between the oesophagus and the 
rectum. 
What tissues in the body are developed from the 
hypoderm ? 
From the hypoderm is developed the epithelium 
lining the alimentary canal and the glands opening 
into it. 
What tissues in the body are derived from the mes 
oderm ? 
From the mesoderm are derived all of the connective 
tissues, blood, bone, fibrous tissue, tendon, etc., the 
muscles and the dentine and cementum. 
What is the first indication of the formation of 
teeth in the embryo ? 
A thickening of the epithelium along the arch which 
is to form the jaw, marking out the arch of the tem- 
porary teeth. This is known as the dental ridge. 
How early does it appear? 
The thickening of the epithelium begins as early as 
the fourth week. 
Describe the formation of the dental ridge. 
The dental ridge appears very early in foetal life, 
simply as a thickening of the epithelium on the arch 
which is to form the jaw. As the cells multiply they 
not only rise above the level of the membrane, but 
sink down below it into the mesodermic tissue below, 
forming what is called the dental groove, the elevation 
being called the dental ridge. EMBBYOLOGY. 
199 
Trace the formation of the enamel organ from the 
dental ridge. 
The dental ridge thickens with a characteristic fold- 
ing, and grows down into the tissue beneath. At ten 
points along the ridge the cells grow down into the 
tissue below in the form of a thread, which becomes 
bulbous or club shaped on the deep end, then the bul- 
bous end becomes invaginated, forming the enamel 
organ. 
Describe the fully formed enamel organ. 
The enamel organ is a double layered bag, made up 
of an outer layer of epithelial cells called the outer 
tunic, an inner layer of epithelial cells called the inner 
tunic, and a stellate reticulum made up of large stellate 
or round cells which form a rather open tissue, filling 
the space between the two tunics. The thread con- 
necting the enamel organ with the dental ridge is 
broken and the fully formed enamel organ is left cov- 
ering the dental papilla. 
Describe the dental papilla. 
The dental papilla is a cone-shaped papilla of meso- 
dermic connective tissue which grows up into the 
invaginated enamel organ so that the inner tunic is 
immediately in contact with the surface of the papilla 
which is covered by the layer of odontoblasts. The 
function of the papilla is to form dentine, and the rem- 
nant of it inclosed in the dentine is persistent as the 
dental pulp. 
What are the ameloblasts? 
The ameloblasts are the columnar cells of the inner 
tunic which form enamel. When they first appear 
they are in contact with the odontoblasts. The odont- 200 
DENTAL HISTOLOGY. 
oblasts form the dentine beginning from the outside 
and forming inward, the ameloblasts form the enamel 
beginning from the inside and forming outward. The 
first formed layer of dentine is the outermost layer of 
dentine, the first formed layer of enamel is the inner- 
most layer. 
In which tunic are the ameloblasts found ? 
In the inner tunic. 
What is the function of the stellate reticulum ? 
Dr. Williams’ work seems to show that the stellate 
reticulum performs the function of a gland providing 
the ameloblasts with the material for the calcification 
of the enamel. 
Describe the formation of the enamel organ for the 
permanent teeth. 
When the enamel organ for the temporary teeth is 
formed, a thread of cells grows down from the band 
which connects the organ with the dental ridge to form 
the enamel organ for the permanent tooth, in the same 
way that that for the temporary one was formed; but 
as there are eight teeth on a side in the permanent set 
and only five in the temporary, three enamel organs 
must take their origin from the dental ridge directly; 
this usually occurs along the posterior part of the 
ridge forming the organs for the permanent molars. INDEX 
Absorption 190 
Ameloblasts 199 
growth 4 
gustatory 71 
Arteries 44 
parietal 78 
Bailiarger, stripes of 150 
Bellini’s tubes 94, 9S 
Cementoblasts 189 
Cementum 173-176 
Bertini’s columns .. .. 92 
Bladder 9 7 
function 174 
structure 174 
Blood 48 
Blastoderm 197 
Cerebellum 157 
Cerebral ganglia 151 
Bone 17 
corpuscle 22 
Cerebrum 148 
Ceruminous glands 139 
developmental phases .. 23 
endochondral 22, 23 
intermembranous 23 
Circulatory system 41 
Clark’s column 142 
Cohnheim’s areas 27 
Brain 148 
periosteal 22, 23 
Corium 132 
Corpuscle Golgi 139 
Brain sand 154 
Bronchi 125 
Corpuscles of Vater 37 
Corpuscles, tactile 35, 36 
Capillaries 47 
Ce115.... 
Corpuscles, blood 49, 50 
Corpuscles of Hassal 57 
bone 18, 19 
Crusta petrosa 173 
cartilage 16, 22 
central 78 
Cuticula dentis 163 
Demilunes of Heidenh in. . .61 
ciliated g, 11 
columnar 10 
Dental papilla 197 
Dental ridge 198 
division of 5 
essential parts. 2 
Dental tissues 159 
Dental ligament 187 
endothelial 12 
fat 15 
Dentine 167-172 
first type 31 
names for 167 
composition of 168 
form 4 
goblet 11 
effect of acid on 168 
granular layer of 170 
201 202 
INDEX. 
secondary 171 
Larynx 121 
Dentinal tubuli.. ..168, 169, 170 
tubuli of 168, 169, 170 
Liver 85 
Lungs 125 
Duct of Bartholin 63 
Dura mater 155 
Lymphatic system 51 
Male reproductive organs. ..101 
Embryology 195-200 
Marginal zone 10 
Enamel 161 
defined 195 
Maturation 196 
Membrana eboris 176 
Enamel dors 162, 163, 164 
Enamel organ 199 
Mesoblast 197 
Moll’s glands 139 
End bulbs 36 
End plates 39 
Mucous membrane 58 
Muscle 24 
Endothelium of Debove 82 
Epiblasts 197 
nerve supply 25 
sarcolemma 25 
Epiglottis 122 
striation 25 
Exostosis 176 
Fallopian tube 113 
Nails ... 134 
Narceous layer of enamel.. 162 
Fecundation 196 
Female reproductive organs 109 
Nasmyth’s membrane 163 
Nerve endings 134 
Fibres 
medullated 32 
in blood vessels 40 
glands 40 
non-medullated 32 
sensory 34 
smooth muscle 38 
nerve 31 
Remak’s 32 
striated muscle 38 
Fibres of Tomes 168 
Sharpey’s 20 
Neuroblasts 28 
tendons 39 
Fibroblasts 188 
Gastrula 196 
neuroglia 34 
nodes of Ranvier 33 
German, stripes of 150 
Glands 58 
Neuron 29 
neurodendron 29 
Cowper’s 107 
intestines 83 
Nucleus 2 
nucleolus 4 
Glisson’s capsule 86 
Odontoblasts 178 
Granular layer of Tomes.. .170 
Hair 135 
Oesophagus 75 
Osteoblasts 188 
Hypoblast 197 
Heart 42 
Osteoclasts 188 
Ovary .109 
Incremental lines of Salter. 171 
Inter-globular spaces 171 
Ovum 195 
Paniculus adiposus 133 
Intestines 81 
Pancreas 88 
Kidney 91 
Papillae 58 INDEX. 
203 
Parovarium 112 
Salivary glands 62 
Perceptive apparatus 41 
Peridental membrane. ..183-194 
action in movement of 
Schmidt-Lantermann seg- 
ments 33 
Sebaceous glands 138 
the teeth 181 
absorption by 190 
Secondary dentine 171 
Segmentation 196 
blood supply 192 
changes with age 193 
cellular elements of.iBB, 182 
Semen 106 
Sheath of Newmann 169 
divisions of 185 
Skin glands 138 
Skin 131 
defined 183 
formation of cementum .189 
Sole plate 39 
Spinal cord 141, 142, 143 
functions of 183 
Spinal nerve roots 142 
glands 192 
indifferent fibrous tissue. 185 
Spleen 55 
Sperm 196 
names for 183 
principal fibres 185 
Stomach 77 
Stratification of enamel 164 
Penis. 101 
structural elements of.. 184 
Sudoriparous glands 139 
Supra renal body 156 
Periosteum 20 
Peyer’s patches 84 
Sweat glands 139 
Telolemma 38 
Pharynx 73 
Testicle 102 
Pia mater 155 
Pineal body 154 
Thymes body 56 
Thyroid body .61 
Pituitary body 154 
Pleura 129 
Tissues 
elemental 2 
Plexus of Auerbach 80 
Plexus of Meissner 80 
epithelial 6 
connective 13 
Prickle cells 131 
lymphatic 52 
Principal fibres of the peri- 
dental membrane 185 
muscular 24 
nervous . 28 
Prostate body 106 
Purkinje, cells of 150 
Tongue 69 
vegetative .2 
Pulp 177-182 
blood supply of 180 
Tonsils 73 
Trachea 123 
cells of 177, 178 
functions of 179 
Uterus 114 
Ureters 97 
nerves of 182 
Urethra 98 
odontoblasts 178 
pathology of 181 
Vagina and genitals 118 
Veins 46 
Respiratory system 121 
where found 177 
Villi 58 
Volkman’s canals 21