SYLLABUS OF LECTURES 
ON 
HUMAN EMBRYOLOGY 
AN INTRODUCTION TO THE STUDY OF 
OBSTETRICS AND GYNAECOLOGY. 
For Medical Students and Practitioners. 
WITH A GLOSSARY OF EMBRYOLOGICAL TERMS. 
BY 
WALTER PORTER MANTON, M.D., 
Professor of Clinical Gynaecology and Lecturer on Obstetrics in the Detroit 
College of Medicine ; Fellow of the Royal Microscopical Society, 
of the British Zoological Society, American Microscopical 
Society, etc., etc. 
Illustrated cuith f4umerous Outline Dracuings. 
PHILADELPHIA: 
THE F. A. DAVIS CO., PUBLISHERS. 
LONDON: 
F. J. REBMAN. 
1894. COPYRIGHT, 1894, 
BT 
THE F. A. DAVIS COMPANY. 
[Registered at Stationers’ Hall, London, England.] 
Philadelphia, Pa., TJ.S.A.: 
The Medical Bulletin Printing-House, 
1916 Cherry Street. TO 
O. BUTSCHLI 
AND 
F. BLOCHMANN, 
HEIDELBERG. PREFACE. 
The object of this syllabus is to furnish to students 
of medicine and practitioners an outline of the principal 
facts in human Embryology ; details and theories must 
be sought for in the works of reference and special 
monographs elsewhere mentioned. 
The book has been so arranged that it ma}r be used in 
the class-room, the printed headings serving as a guide 
during the elaboration of the subject by the teacher; 
notes of the lecture are to be taken down at the time on 
the blank pages provided. Sufficient space has been left 
around each outline cut so that the student majT himself 
write down the names of the parts, thereby helping to 
fix them in his memory. 
The general arrangement followed is that adopted 
in my lectures for the past ten years. In the revision 
of my notes the latest editions of the following works 
have been consulted: His: “Anatomie menscldicher 
Embryonen.” Kolliker: “ Entwickelungsgeschiclite der 
Menchen und der Hoheren Thieren.” Yon Baer: 
“ Entwickelungsgeschiclite.” Bonnet: “ Grundriss der 
Entwickelungsgeschiclite der Haussaugethiere.” O. 
Hertwig: “ Lehrbuch d. Entwickelungsgescliichte d. 
Menchen und d. Wirbeltliiere.” Balfour: “ A Treatise 
on Comparative Embryologj’.” Foster and Balfour: 
“Elements of Embryology.” Haddon : “An Introduc- 
tion to the Study of Embryology.” Minot: “ Human 
Embryology.” 
Besides these, current medical literature and espe- 
cially the“ Journal of the Royal Microscopical Society,” 
V VI 
PREFACE. 
“ Archiv fur Gynakologie,” “ Zeitschrift fur Geburts- 
liulfe und Gynakologie,” and works on zoology, anat- 
omy, physiology, obstetrics, and diseases of women 
have been drawn upon. 
For the benefit of those who may desire to read up 
on special subjects, reference foot-notes have been added. 
The outline drawings, partly diagrammatic, have been 
taken from various sources, as far as possible acknowl- 
edged, and from the specimens in my own collection 
which are used for class illustration and demonstration. 
I desire here to express my thanks to my friend, 
Dr. E. H. Sargent, Lecturer on Bacteriology in the 
Detroit College of Medicine, for many suggestions in 
the preparation of this syllabus. 
W. P. M. 
Detroit, August 1, 1894. CONTENTS. 
SECTION I. 
PAGE 
Introduction 1 
SECTION II. 
Anatomy of the Female Organs of Generation . 6 
SECTION III. 
The Spermatozoon ; Spermatogenesis—The Ovum, 
Oogenesis, Menstruation 25 
SECTION IV. 
The General Development of the Embryo .... 36 
SECTION Y. 
The Uterine and Fietal Membranes ; the Placenta 
AND UTERO-PLACENTAL CIRCULATION 45 
SECTION VI. 
The Deyelofment of Special Organs and Parts— 
the Heart, Blood-vessels, and Blood .... 53 
General Consideration of the Child at Birth . . 86 
SECTION YII. 
SECTION VIII. 
Changes in the Maternal Organism Incident to 
Pregnancy 91 
SECTION IX. 
Practical Work 95 
A Glossary of Some of the Words and Terms Used 
in Embryology 113 
Index 121 
VII SOURCES FROM WHICH ILLUSTRATIONS HAVE 
BEEN DERIVED. 
Balfour, Fig. 26. 
Barnes, “ Obstetric Medicine and Surgery,” Fig. 35. 
Bonnet, Figs. 30, 43, 47, 48, 49, 57. 
Bumm, “ Archiv fur Gynakologie,” Bd. xliii, Fig. 36. 
Claus and Sedgwick, Figs. 2, 4. 
Francis, Figs. 66, 67. 
Henle’s “ Anatomie,” Figs. 6, 7, 10,11,12. 
Herting, O., Figs. 18. 19, 20, 33, 37, 55, 62, 64. 
His, Frontispiece and Figs. 34, 38, 39, 40, 53, 59, 60, 61. 
Kolliker, Figs. 42, 63. 
Manton, Figs. 1, 8, 24, 29, 32, 44, 65, 68, 69. 
Minot, Figs. 25, 45. 
Packard’s “ Zoology,” Fig. 3. 
Quain’s “Anatomy,” Figs. 5, 15,17, 22, 23, 31, 58. 
Ranney, “Topographical Relations of the Female Pelvic Organs,” 
Fig. 9. 
Sutton, Bland, “ Surgical Diseases of the Ovaries and Fallopian 
Tubes,” Figs. 14, 16. 
VIII OF 
Lectures on Human Embryology. 
SECTION I. 
Introduction 
Embryology (Greek, Efifipvov, embryo, and Xoyog, 
a discussion) is an important subdivision of Biology 
treating of “ those successive modifications through 
which the organism passes in its development from the 
germ to the adult-form.”1 Alike important in the study 
of Natural History, Physiology, and Obstetrics. 
The term Embryo, later Foetus, is applied to the 
unborn young, which at birth may resemble the parent 
form,—e.g., mammals ; or, as in some of the lower orders 
of life, must undergo a series of changes and modifica- 
tions before attaining to the adult state,—e.g., frog. 
The study of Embryology is divided into two parts, 
one of which, called “Ontogeny ” (av, existence, and 
ysvquo, to beget), deals with the history of the indi- 
vidual and the development of the animal and its 
various parts; the other, called “Phytogeny ” (<pv?*og, 
race, and yevao, to beget), compares the development 
of different animals, and “ attempts therefrom to deduce 
or reconstruct the evolution of the Animal Kingdom.” 
The Animal Kingdom is composed of Protozoa, or 
unicellular animals,—e.g., Amoeba; and Metazoa, or 
1 Spencer’s Biology, vol. i, p. 97, 
1 2 
HUMAN EMBRYOLOGY. 
animals composed of many cells so united as to form 
tissues,—e.gr., all animals,—and which alone produce 
eggs (ova). 
Fig. i. 
Propagation of Species.—Four methods : (a) Fission. 
The organism divides into two similar parts,—e.g., the 
amoeba; white blood-corpuscle. 
Fig. 2. 
(b) Budding, or Gemmation. The organism devel- 
ops outgrowths, which finally become separated from 
Fig. 3. 
the parent, and carry on a separate existence,—e.gr., 
hydra. INTRODUCTION 
3 
(c) Spore Formation. The organism breaks up into 
a considerable number of parts, each of which resembles 
the parent form,—e.g., protomyxa. » 
(d) Conjugation and Fusion. The uniting and fusion 
Fig. 4. 
of two dissimilar organisms,—e.g., ovum and sperma- 
tozoon. 
Sexual Development.—Puberty: Twelfth to fifteenth 
year in the female, usually somewhat later in the male. 
Fig. 5. 
Changes in the Organism.—Male: Growth of pubic, 
abdominal, and axillary hair; change in pitch and vol- 
ume of voice ; sexual activity ; formation and ejaculation 4 
HUMAN EMBRYOLOGY. 
of spermatic fluid with spermatozoa. Female: Change 
in figure, rounding of limbs, development of mammary 
glapds ; growth of pubic hair; sexual activity, monthly 
discharge from genitals (menstruation), periodical dis- 
charge of ova. 
Function of the Male.—Production of fertilizing cell 
for conjugation and fusion with the female egg-cell. 
The term Genoblast is applied to the mature element 
of either sex. 
Fig. 6. 
Male Reproductive Glands.— Testicles: These are 
ovoid bodies, paired, slightly compressed laterally, 
inches long, inches wide, and 1 inch thick; weight, 
| to 1 ounce. The left is usually larger than the right. 
They are suspended in the scrotum by the spermatic 
cord and membranes. Anatomy: Tunica vaginalis, T. 
albuginea, corpus Higlnnori, trabeculae, tunica vasculosa, 
tubuli seminiferi, tubuli recti, rete vasculosum, vasa 5 
INTRODUCTION. 
efferentia, epididymis, vas deferend, seminal vesicles, 
seminal or ejaculatory ducts.1 
Secretion of the Testicles (Seminal Fluid, Semen).— 
A thick, viscid fluid, containing spermatozoa, squamous 
and columnar epithelium, seminal granules. Chemistry 
of semen: Reaction neutral or alkaline; 82 per cent. 
Fig. 7. 
water; serum-albumin, alkali albuminate, nuclein, leci- 
thin, cholesterin, fats, pliosphorized fats; salt, 2 per 
cent., especially phosphates of the alkalies and earths; 
together with sulphates, carbonates, chlorides, and sper- 
matin.2 
1 Quain’s Anatomy, 9th ed., p. 685. 
3 Landois’s Human Physiology, p. 859. SECTION II 
Anatomy of the Female Organs of Generation. 
The Vulva.—This comprises all that part of the 
genitals visible to the eye when the subject is in the 
dorso-recumbent position with thighs flexed and knees 
widely separated. The vulva (valve to vagina, V. con- 
fig. 8. 
nivens, V. hians) includes the following parts: Mons 
Veneris, Labia Majora and Minora, Clitoris, Perineum, 
Fourchette, and Vestibule. 
Mons Veneris.—This is a triangular space tying in 
front of the pubic symphysis, and forming the superior FEMALE ORGANS OF GENERATION. 
boundary of the labia majora. It consists of a pad 
of fat with areolar tissue and integument, and is cov- 
ered, after puberty, with coarse hair, which has a ten- 
dency to curl. Its apex is toward the labia majora 
and its base is bounded by the hypogastric fold. The 
skin contains sweat-glands and numerous sebaceous 
follicles, which give rise to an oily feel of the parts. 
Function unknown ; acts, perhaps, as a buffer to the 
male pubis during coitus. 
Labia Majora (Greater Lips).—Lateral cutaneous 
folds extending from mons veneris to perineum, where 
they are united by the anterior and posterior commis- 
sures, forming the lateral boundary of the vulva-cleft. 
Homologue of male scrotum. The lips are thicker an- 
teriorly than posteriorly, and receive the terminal fibres 
of the round ligaments. The external surface of the 
labia consists of integument of a darker color than that 
of the body, and is covered by hair after puberty. On 
the internal surface the integument is rosy and covered 
by downy hair. The lips are approximated in virgins, 
but are separated in old women. 
Structure.—On section the great lips have a trian- 
gular shape, and internally consist of elastic fibres ar- 
ranged in the form of a sac (dartos), fat, and large 
blood-vessels. The skin contains large hair-bulbs and 
sebaceous follicles. The labia are in relation, during 
early life, with the inguinal canal, which closes from 
the twentieth to the thirtieth day after birth.1 An 
open canal (canal of Nuck) may give rise to hernia of 
intestines, ovary, uterus ; hydrocele.2 
1 J. H. Warren, Practical Treatise on Hernia. Marcy, Anatomy and 
Surgical Treatment of Hernia, p. 29. 
5 Barber, Transactions of the Michigan State Medical Society, 1891, 
p. 324. Thomas and Munde, Diseases of Women, vol. ii, p. 141. Pozzi, 
Medical and Surgical Gynaecology, p. 188. 8 
Arteries, superficial perineal branch of Internal 
Pudic. 
Veins, rich plexus communicating with Bulb of 
Vagina. 
Lymphatics enter superficial Inguinal glands. 
Nerves, superficial perineal branch of Internal Pudic, 
inferior branch of small Sciatic. 
HUMAN EMBRYOLOGY. 
Labia Minora (Nymphse, Smaller Lips).—“Muco- 
cutaneous folds ” hidden under greater lips in the vir- 
gin. Above, meet and bifurcate to form frenulum and 
prepuce of the Clitoris; below, appear to blend with 
labia majora at about their middle, but re-appear farther 
down, and are united by the Fourchette behind. 
Color, red in virgins, darker in adults and aged ; 
may resemble, in form and color, a cock’s comb. 
Structure—arteries, Areins, etc.—derived as in labia 
majora. Numerous sebaceous follicles. 
Nerves have “ end bulbs.” 
Function, supposed to bring penis and clitoris in 
close apposition and to direct the stream of urine 
(nymphse,—so called from mythological nymphs which 
presided over fountains). Hottentot apron (Cuvier), 
six to eight inches long.1 
Vestibule (Latin, Vestibulum).—Triangular space: 
apex, below clitoris; base, anterior margin of vaginal 
mouth; sides, formed by nymphse. Covering, corru- 
gated mucous membrane. Pierced in the middle line, 
about one inch below the clitoris, by the urethra (Mea- 
tus urinarius). Contains Qlandulse vestibulares minores, 
—minute, five or six,—which ma}' attain to one-third 
the size of meatus. 
Arteries, from Pudic. 
Veins, from Pudic, Pars intermedia, Isthmus, above 
1 Hyrtl, Anatomie des Menscben, p. 792. FEMALE ORGANS OF GENERATION. 
9 
and below meatus, uniting in Bulb of Vagina (Corpus 
cavernosum urethrse,—Savage). 
Nerves, from Pudic. 
Bulb of Vagina.—An oblong body, net-work of 
veins, “ erecto-tnrgescent tissue,” situated on either 
side of vestibule. Extends from root of clitoris to 
lower third of vaginal orifice. About one and one-half 
inches long by half an inch at lowest end (Savage). 
Free communication of veins with opposite side,—veins 
of clitoris, labia, perineum, vagina, obturator plexus, 
epigastric. 
Arteries, from Internal Pudic. 
Nei'ves, from Sympathetic. 
Vulvo-Vaginal Gland (Glands of Bartholin, Tiede- 
man, Duvernay, Cowper).—Reddish-yellow body, size 
of bean, about one-half inch long; one on either side 
of vagina at lower end of bulb. Duct one-half to 
three-fourths of an inch long; opens on inner surface 
of nymphae, in front of base of hymen. Secretion 
thin, penetrating odor. 
Use, to lubricate vaginal orifice during coitus; fluid 
sometimes ejaculated in jets; thought by the ancients 
to be similar to semen. 
Perineum (Greek, 7lepi, around ; vaiov, a temple).— 
An irregularly quadrilateral body forming part of sa- 
cral segment of pelvic floor.1 Extends from divergence 
of rectum and vagina to vulvo-anal space. Measures 
about one and one-fourth inches vertically, one and one- 
fourth inches transversely, three-fourths inch antero- 
posteriorly. Formed of muscles and fascia. 
1 Hart, Structural Anatomy of the Female Pelvic Floor, 1880. Marcy, 
The Perineum. 1889. Agnew, Laceration of the Female Perineum, 1879. 
Bantock, Treatment of Ruptured Perineum, 1878. Olshausen, “Ueber, 
Dammverletzunge und Dammschutz,” Volkmann’s Klinische Vortrage, 
No. 44. Garrigues, American Journal of Obstetrics, April, 1880. 10 
HUMAN EMBRYOLOGY. 
Muscles. — Bulbo-cavernosus, Transversus perinaei 
(superficial and deep), Sphincter ani, Levatores ani. 
Median raphe (central tendon) may become almost 
cartilaginous in old persons. “ If a straight line be 
made to join the tip of the coccyx and the subpubic 
ligament, it will just clear the apex of this structure.”1 
Importance of perineal body greatly overestimated; 
not a key-stone supporting parts above. The Levator 
ani is the great supporting muscle and constrictor of 
the vagina. Tears of this and the neighboring fascia 
during childbirth destroy the integrity of the pelvic 
floor and give rise to a train of genesic ills. Repair of 
this muscle most important; stitching of perineal skin 
least important.2 
Arteries.—Inferior Haemorrhoidal, Transversus pe- 
rinaei, Superficial Perineal, from Internal Pudic. 
Veins terminate in Pudic veins. 
Nerves, from Pudic, small Sciatic, fourth Sacral. 
Lymphatics unite with those of external genitals 
and enter Inguinal glands.3 
Fig. 9. (See Fig. 10.) 
Urethra.—A narrow musculo-membranous canal 
1 Hart and Barbour. 
3 Emmett, Principles and Practice of Gynaecology. 
* Ranney, “The Female Perineum,’’ New York Medical Journal, 1882. FEMALE ORGANS OF GENERATION. 
11 
buried in anterior vaginal wall, extending from bladder 
to meatus, slightly curved, concavity upward, held in 
position by pubo-vesical ligament. About one and one- 
half inches long, diameter one-fourth to one-third inch, 
funnel-shaped, posterior wall dilated above meatus. Two 
coats,—mucous, muscular. Mucous follicles and glands. 
Very dilatable (coitus; urethrocele). 
Meatus, external orifice of urethra, puckered, promi- 
nent mucous margin. Mucous glands. Skene’s glands.1 
Jet of urine larger than in male. Tears may occur 
during parturition or passing the catheter. 
Arteries.—Vaginal, Internal Pudic, and the uterine 
branches; from Internal Iliac. 
Veins, urethral plexus,—the u true erectile plexus ” 
(Savage) ; from Internal Iliac. 
Nerves, from hypogastric plexus of Sympathetic, 
fourth Sacral, Pudic of Spinal. 
Lining, mucous membrane,—pavement variety of 
epithelium below, “ transitional ” above. 
Fourchette.—A delicate fold of skin uniting the pos- 
terior extremities of the nymphse, situated above pos- 
terior commissure 2.5 to 2.7 centimetres. With labia 
in apposition the fourchette bags downward ; when the 
former are stretched apart its free border appears as a 
tense, whitish band. A space exists between the four- 
chette and the posterior commissure,—Fossa Navicu- 
laris,—an artificial depression. Frequent seat of con- 
dylomata. 
Arteries, veins, and nerves as in labia. 
Anterior and Posterior Commissures.—The junction 
of large lips with mons veneris anteriorly and with each 
other posteriorly. Not transverse connecting bands 
(Luschka). 
* Skene, Diseases of the Bladder and Urethra in Women. HUMAN EMRRYOLOGY. 
The female internal sexual organs comprise the 
Hymen, Vagina, Uterus, Fallopian tubes, and Ovaries. 
INTERNAL ORGANS. 
Hymen.—Formed by a folding in of entire vaginal 
wall. Double fold of mucous membrane containing 
vessels and nerves. Continuous with vaginal wall pos- 
teriorly, free margin anteriorly. Partially closes va- 
ginal ring. Perforated, for escape of discharges, above 
centre. Normally, in erect position of bod}r, the hymen 
lies loosely against posterior vaginal wall. It is usually 
Fig. 10. 
ruptured at first intercourse, but be so tough as to 
prevent act. May persist even after birth of premature 
(seven months’) child (Ranney). Opening generally 
crescentic (II. semilunaris) or round (II. annularis), 
sometimes several perforations (II. cribriformis) or 
with fringed borders (H. fimbriatus). Complete clos- 
ure is pathological (H. imperforatus). 
or absent, not uncommon. The ancients considered 
the hymen a mark of virginity. Some of the ungulata, 
the ruminata, carnivora, and monkeys have an analo- 
gous membrane. FEMALE ORGANS OF GENERATION. 
13 
Carunculee myrtiformes are not remains of the 
hymen. 
Blood-vessels and nerves, from those supplying the 
vagina. 
Vagina (Latin, Vagina).—A museulo-membranous 
tube lying between bladder and rectum, extending from 
external orifice to uterus. It is attached below to the 
iscliio-pubic rami, continuous above with the neck of 
the uterus. Somewhat contracted at lower extremity. 
H-shaped on section. 
Fig. ii. 
Direction slightly curved,—sixty degrees to plane 
of horizon. Two walls, anterior and posterior. 
Length of anterior wall inches, of posterior wall 
inches. 
Walls in apposition, not an open canal. Three lay- 
ers,—mucous, muscular, and connective tissue. Thick- 
ness varying according to amount of muscular tissue 
present. 
Columns of vagina most marked on anterior wall. 
May be divided. 14 
HUMAN EMBRYOLOGY. 
Anterior Wall, firm connection with urethra, lower 
half (urethro-vaginal septum). Less firm connection 
above with bladder (vesico-vaginal septum). Contains 
vesico-vaginal plexus of veins. Anterior cul-de-sac 
shallow. 
Posterior Wall joins anterior lip of cervix high up. 
Separated from rectum in upper fifth by cul-de-sac of 
Douglas. Loosely attached in space between cul-de-sac 
and perineal bod}- (recto-vaginal septum). 
Mucous membrane consists of connective tissue, 
elastic fibres, and pavement epithelium. 
Arteries, Vaginal, Uterine, Internal Pudic, from 
Internal Iliac. 
Veins rich, valveless. Plexuses communicating with 
neighboring plexuses. 
Lymphatics,lower part,enter Inguinal glands; upper 
part, internal Inguinal glands. Lymph-follicles.1 
Nerves, Hypogastric (sympathetic), Fourth Sacral, 
Pudic (spinal). 
Uterus (Greek, iKTTfcpov).—A hollow,muscular, pear- 
shaped organ or “ inverted, truncated cone,” flattened 
from before backward. Receptacle and nidus of im- 
pregnated ovum up to time of expulsion (labor). 
Length, to 3 inches; cavity, 2 to inches; 
breadth, widest, 2 inches; isthmus, 1 to inches ; 
thickness, 1 inch; of walls, inch; weight, 1 to 12 
drachms (virgins). 
Situation, middle of pelvic cavity, between bladder 
and rectum. 
Position, slight anteflexion,2 varying according to 
state of distension of bladder and rectum. Mobility 
considerable ; motion during respiration. 
1 Lowenstein, Centralblatt f. Med. Wissenscli., p. 546, 1871. 
51 Schultze, The Pathology and Treatment of Displacements of the 
Uterus, translated by Macan, 1888. FEMALE ORGANS OF GENERATION. 
15 
Parts, three,—cervix, body, and fundus. 
Cervix (vaginal portion), in young virgins, about 
one-third inch long; longer and larger in nulliparous 
and those who have borne ; nearly flush with vaginal 
vault in senile. Variable shape,—conical in virgins. 
Partly projects into vaginal canal. A central dimple 
or transverse slit is the Os externum (os tine®, mouth 
of tench-fish). Feel, in virgins, similar to that con- 
veyed to finger by pi’essing tip of nose. Anterior and 
posterior lips : consistency, hard in virgins, softer in 
Fig. 12. 
those who have borne children and in disease. Gener- 
ally lacerated during childbirth. “ The end of the cer- 
vix marks nearly the centre of the pelvic cavity, the 
centre of a radius of about two inches ” (Savage). The 
cervix is separated from the body by the Isthmus,—a 
slight constriction at the Os internum. 
Body extends from isthmus to fundus, tapering from 
above downward. It is softer in consistence than the 
cervix. Its length is nearly two inches, the anterior 
surface being flattened, while the posterior is more 
convex. At the upper angles are the openings of the 
Fallopian tubes. 16 
HUMAN EMBRYOLOGY. 
Fundus, the free convex upper portion of the uterus 
above the openings of the Fallopian tubes. It lies 
slightly below the plane of the pelvic brim, and is cov- 
ered with peritoneum. The uterus is suspended later- 
ally by the Broad Ligaments, along the upper margin of 
which run the Fallopian tubes; the Bound Ligaments 
and Vesico-uterine Folds anteriorly, the Sacro-uterine 
Ligaments posteriorly (Musculus retractor uteri,— 
Luschka), and the Pelvic B'ascia. 
Structure, three layers, from inward without,—a 
mucous, a muscular (three layers, chiefly unstriped 
muscle), and a serous (peritoneum).1 
Cavity of Cervix (cervical canal) extends from os 
externum to isthmus, fusiform in virgins, more tubular 
in the parous. The lining is thrown into folds, giving 
rise to the anterior and posterior ridges (Palmse Plicatse 
or Arbor vitae). In the cervix the mucosa is firmer and 
more fibrous than in the body. Columnar epithelium 
lines the upper part, stratified cells the lower. The 
mucosa contains cylindrical and goblet glands and the 
so-called ovida Nabothi.2 
Cavity of the Body.—The cavum uteri extends from 
the isthmus to the fundus. Form triangular, with con- 
vex sides. Base above, with minute openings of the 
Fallopian tubes at the angles. Apex at isthmus. The 
mucosa of the body is smooth, devoid of ridges, spongy 
(muscularis mucosae). It is lined with ciliated colum- 
nar epithelium, and contains the utricular glands. 
The so-called globus hystericus, the peculiar feeling in 
the throat which often ushers in an attack of hysteria, 
* Ercolini, Tlie Reproductive Process, translated by Marcy, 1884. 
g According to Hyrtl, Martin Naboth, professor in Leipzig, an other- 
wise unknown man, attempted to give to these vesicles, which the anato- 
mists held to be hydatids, the same importance as the ovaries. (Lehrbuch 
der Anatomie des Menschen, 1881.) FEMALE ORGANS OF GENERATION. 
17 
was supposed by the ancients to be due to the womb 
rising into the throat. From this the name of this 
nervous condition was derived. 
Arteries, four,—two Ovarian (spermatic in the male), 
from Abdominal Aorta; two Uterine, from anterior di- 
vision of Internal Iliac. “ Curling arteries.” Circular 
artery. 
Blood-vessels of the cervix distinguished by the great 
thickness of their walls. 
Veins.—Venous plexuses, sinus-like in middle layer, 
communicate freely with Vaginal, Vesical, Pampiniform 
plexuses, and terminate in Internal Iliac and Ovarian 
veins. 
Nei'ves arise chiefly from inferior Hypogastric plexus, 
Sperniatic plexus, and third and fourth Sacral nerves.1 
Lymphatics unite with those from the tube and the 
ovary to form an extensive net-work in the broad liga- 
ment and enter the lumbar glands. The lymphatics of 
the cervix and upper three-fourths of the vagina open 
into the Hypogastric glands, or Obturator glands.2 
Fallopian Tube (Oviduct).—A sinuous tube, one on 
either side, extending from the angle of the uterus, in- 
closed in upper free margin of broad ligament, extend- 
ing outward to the pelvic brim. Length, from 3 to 6 
inches, the right usually slightly longer than the left. 
Course, outward, backward, inward (shepherd’s crook). 
Three parts : Isthmus, narrowest portion, diameter 2 to 
3 millimetres, cord-like, extends through uterine wall 
to ampulla. Lumen at uterine ostium minute, admits 
only a fine bristle. Ampulla, dilated portion of the tube, 
diameter 6 to 8 millimetres, extends to fimbriated portion 
1 Frankenhauser, Die Nerven tier Gebarmutter und ihre endigung in 
den glatten Muskelfasern. Jena, 1867. 
a Leopold, “Die Lymphgefasse ties normalen, nicht Scliwangereii 
uterus,” Arcliiv f. Gynakologie, Bd. vi, p. 1, 1874. 18 
HUMAN EMBRYOLOGY. 
(also called infundibulum, pavilion). Abdominal mouth 
of the tube called the ostium abdominale, morsus diaboli.1 
Infundibulum, trumpet-shaped. It has four or five 
fimbriae, which have been compared to the tentacles 
of the sea-anemonae. The serous membrane of the 
peritoneum and the mucous membrane of the tube join 
at this point, the only instance of the kind in the human 
Fig. 13. 
body. One of the long, finger-like processes of the in- 
fundibulum extends to the ovary (fimbria ovarica). A 
small cyst called the Hydatid of Morgagni is often seen 
hanging from one of the lower fimbriae of the tube. 
This represents the blind extremity of Miiller’s duct. 
1 A plant which, on account of its astringent properties, was much 
used for healing wounds and sores was called Scabiosa succisa. Its rav- 
eled-out roots appeared as if gnawed off (Radix prcemorsa), and it was 
supposed that the devil, annoyed at the good service which the plant had 
rendered man, had bitten them off in anger. The older anatomists in 
Germany, France, and Holland, down to the time of Haller, were also 
professors of botany (anatomists in winter, botanists in summer), and 
from them the abdominal end of the Fallopian tube came to be known as 
the morsus diaboli, from its fancied resemblance to the root of the plant. 
(Hyrtl, Anatomy, p. 786.) FEMALE ORGANS OF GENERATION. 
19 
Structure of Tube.—Three layers,—serous (perito- 
neal) ; muscular, consisting of circular and longitudinal 
fibres; and mucous. This membrane is thrown into 
longitudinal folds, most numerous in the ampulla (Arbo- 
rescent processes). The lining is of columnar epithelium. 
Use, to convey ovum from ovary to uterus. Possibly 
participating in the menstrual function (Lawson Tait). 
The vascular and nei'vcus supply is derived from the 
vessels and nerves supplying uterus and ovaries. 
Ovaries (Latin, Ovarii).—The genital glands are 
flattened, o-void bodies, one on either side of the uterus, 
Fig. 14. (See also Fig. 13.) 
attached to the posterior fold of the broad ligament by 
a straight side (hilus). The opposite border is free and 
convex (oophoron), as are its sides. The end of the 
ovary toward the uterus is smaller and more pointed 
than that directed toward the pelvic wall. 
Size.—This varies in different individuals and at dif- 
ferent periods of life. It is largest during the first six 
weeks after parturition (Henning), and the two are usu- 
ally unequal in size in the same individual. The aver- 
age length is about inches, by f inch wide and f inch 
thick (Farre). The weight is from 60 to 135 grains 
(Hart). 20 
HUMAN EMBRYOLOGY. 
Situation.—The ovary is normally on a level with 
the inlet of the pelvis, behind the Fallopian tube and 
round ligament. It is slung between two ligaments, 
which are attached to either pole. At the uterine, in- 
ternal end is the Ovarian Ligament, a fibro-muscular 
cord about an inch long, running from the side of the 
uterus below the origin of the Fallopian tube. The ex- 
ternal or Inf undibulo-pelvic Ligament is that part of the 
upper margin of the broad ligament unoccupied by the 
Fallopian tube. Above this is the elongated fimbria 
from the infundibulum. 
Position.—This is variable, as the ovaiyr is not a 
fixed organ ; probably oblique to the axis of the pelvis. 
The ovary is in contact with the small intestine on the 
right side, with the rectum on the left. 
Color of the ovary is a pinkish, pearly hue, varying 
to dark purple at menstruation (Tait). 
Structure.—Three layers : (a) An external epithe- 
lial layer, consisting of a single layer of polyhedral 
cells (germinal epithelium).1 Whether this laj'er is dis- 
tinct from the peritoneum of the broad ligament, the 
point of transition being marked by an irregular or 
wave-like line, is still in dispute. Waldeyer, Leopold, 
Klein, and others claim that the surface of the ovary is 
covered by a layer of cells in “ marked contrast to the 
transparent, flattened endothelial plates covering the 
ligamentum latum ” (Klein); while Lawson Tait, on the 
other hand, affirms that the ovary is covered by perito- 
neum, and Bland Sutton states that “ the external cov- 
ering of the ovary is directly continuous with the pos- 
terior layer of the broad ligament.” (h) A firm, fibrous 
layer (tunica albuginea ovarii). (c) Stroma, cortical 
layer, consisting of a fine connective tissue, in which 
1 Waldeyer, Eierstock und Ei. Leipzig, 1870. FEMALE ORGANS OF GENERATION. 
21 
are muscular fibres and many spindle-shaped cells. The 
superficial cortical substance (parenchymal zone) con- 
tains numerous groups of small Graafian follicles (ovi- 
sacs), and, deeper in the stroma (zona vasculosa), iso- 
lated and larger follicles occur. The portion of the 
ovary nearest the hilus (paroophoron) never contains 
follicles (Sutton). 
The blood-vessels, nerves, and lymphatics of the 
ovary find entrance and exit at the hilus. 
Arteries, Ovarian from Abdominal Aorta and branch 
from Uterine. 
Veins, Ovarian. Just below the ovary is a club- 
shaped, venous body, the Bulb of the Ovary (Savage). 
This anastomoses with the uterine and spermatic plex- 
uses, and with them forms the 
Pampiniform Plexus.—This plexus terminates in 
the ovarian vein. The vein of the right side has a 
valve. 
Nerves are derived from the Ovarian plexus and the 
Uterine nerves. 
Lymphatics unite with those from the tube and upper 
part of the uterus and enter the lumbar glands. 
Graafian Follicles.—The smallest of these measure 
about inch and have no proper wall, a single layer 
of cells surrounding the ovum. The larger follicles 
inch) present a basement membrane (membrana 
propria) and an internal lining of columnar epithelial 
cells (membrana granulosa). The ovum is usually situ- 
ated at a point in the follicle farthest from the surface 
of the ovary, and is surrounded by the discus prolig- 
erus. The rest of the follicle is filled with fluid 
(liquor folliculi), which contains paralbumin. The 
most prominent point of the follicle, at which rupture 
will occur, is called the Stigma. From 36,000 to 70,000 HUMAN EMBRYOLOGY. 
follicles are said to exist in the ovary at birth, but no 
authority is given for the statement. 
Fig. 15. 
Parovarium, also called the Organ of Rosenmuller 
and Epi-o'dphoron. Analogous to the epididymis in the 
male. This is a series of tubules situated in the broad 
ligament near the external end of the ovary. Their 
course is parallel and somewhat zigzag as tlie}r spread 
Fig. 16. 
out, fan-like, toward the upper portion of the ligament. 
The apex of the parovarium is at the liilus of the ovary, 
the base a transverse canal, the remains of the duct of 
Gartner, in which the tubules terminate. This canal 
ends in a fine, thread-like structure running toward the 
uterine wall. The number of the tubules varies from FEMALE ORGANS OF GENERATION. 
23 
5 or 6 to 24 (Doran).1 They are the remains of the 
Wolffian bodies. 
Structure.—The walls of the tubules consist of two 
layers of fibrous tissue,—an external circular and an 
internal longitudinal. The lining is ciliated epithelium 
and the contents a clear, coagulable fluid. 
Rectum comprises the lower eight inches of the large 
intestine, extending from the sigmoid flexure to the anus. 
In its entire length it is contained within the true pelvis. 
The rectum begins opposite the left sacro-iliac articula- 
tion, runs obliquely downward from left to right to the 
middle of the sacrum, then curves forward behind the 
cervix uteri and vagina, and again turns downward and 
backward to the anus. The course is therefore some- 
what S-shaped. The upper end of the rectum is smaller 
than the lower, which is dilated into an ampulla. 
Structure.—Three coats,—serous (peritoneal above), 
muscular, and mucous. 
Connections.—The rectum is attached above to the 
uterus, the middle portion anteriorly to the posterior 
wall of the vagina, and below to the perineal body. 
Posteriorly it is attached to the sacrum by folds of the 
peritoneum (mesorectum). 
Arteries.—Superior Haemorrhoidal from Inferior 
Mesenteric, Middle Haemorrlioidal from Internal Iliac, 
Inferior Haemorrlioidal from Pudic. 
Veins are numerous, forming haemorrlioidal plexus. 
They terminate in the Internal Iliac and Mesenteric. 
Lymphatics enter the Sacral and Lumbar glands. 
Nerves numerous, from Sacral plexus of Cerebro- 
spinal, and from Inferior Mesenteric and Hypogastric 
Plexuses of the Sympathetic. 
1 Tumors of the Ovary, Fallopian Tube, and Broad Ligament. Lon- 
don, 1884. 24 
HUMAN EMBRYOLOGY. 
Bladder (Latin, Vesica urinaria).—A hollow, mus- 
cular organ, balloon-shaped when distended, triangular 
or Y-shaped when collapsed; situated between the pubic 
symphysis and the vagina and uterus. The normal ca- 
pacity of the bladder is about a pint, but it is capable 
of great distension.1 There are three openings into 
the viscus,—two for the ureters and one for the urethra. 
The organ is divided, for description, into three por- 
tions,—a body, a base or fundus, and a neck. The 
former is that portion lying above the level of the 
ureters and the centre of the symphysis; the base is all 
the portion below and includes the trigone ; the neck is 
the narrowest portion and surrounds the opening of the 
urethra. 
Structure.—Three layers,—muscular, mucous, and 
peritoneal. The muscular layer varies from one-sixth 
to one-lialf inch in thickness, according to the amount 
of distension. 
Ligaments.—Two sets,—true and false. The true 
ligaments are derived from the vesico-rectal fascia,— 
two anterior and two lateral. The false ligaments, five 
in number, consist of peritoneal folds,-—two posterior 
or recto-vesical; two lateral, from sides of bladder to 
iliac fossse ; one superior, urachus (ligamentum suspen- 
soriurn), extends from top of bladder to umbilicus. 
Arteries.—Superior Vesical from Hypogastric, In- 
ferior Vesical from Internal Iliac, branches from Uter- 
ine, and from Vaginal to neck. 
Veins.—Large plexuses cover the organ and empty 
into the Internal Iliac. 
Lymphatics enter the glands near the Internal Iliac. 
Nerves, from Hypogastric plexus of Sympathetic 
and Sacral Plexus of Cerebro-spinal system. 
1 Man ton, Sudden Emptying of the Bladder as a Cause of Cystor- 
rhagia. SECTION III. 
The Spermatozoon ; Spermatogenesis—The Ovum, 
Oogenesis, Menstruation. 
The Spermatozoon.—The spermatozoon is the small- 
est element of the human body, measuring rather more 
than 0.05 millimetre, and consists of three parts,—a 
head, a middle piece, and a tail. It 
differs in appearance in different 
animals. 
The Head.—In man the head of 
the spermatozoon is a flattened ovoid 
when viewed from above, being 
inch in length and ttsA?to inch in 
breadth (Quain). If viewed from the 
side the head appears somewhat pointed 
or pear-shaped, the larger, thicker end 
being joined to the middle piece. A 
slight concavity on each surface of the 
anterior portion gives a lighter, thinner 
appearance to that part. 
The Middle Piece is about as long 
as the head, and is cylindrical. It is 
wound by a spiral thread, and is often 
rough or granular in appearance. 
The Tail resembles a fine hair or flagellum, and 
gradually tapers to its end. 
Fig. 17. 
Motion.—The spermatozoon is propelled by a circu- 
lar or rotary movement of the tail, the energy being 
propagated from the middle piece. The distance trav- 
ersed by the spermatozoon is estimated to be from 1.2 26 
HUMAN EMBRYOLOGY. 
to 3.6 millimetres per minute (Bonnet), the movements 
being particularly active in normal vaginal secretion. 
Water, alcohol, and various other fluids have a par- 
alyzing effect on the movement, but cold only tempo- 
rarily suspends action; spermatozoa may be frozen 
and thawed several times without apparent injury. The 
average life of the spermatozoa after ejaculation was 
supposed to be only a few days, but it has been recently 
shown that they may retain their vitality in the vagina 
for a period of at least seventeen days, and even through 
a menstrual epoch.1 The same period of vitality ob- 
tains in the domestic fowl; while in the bat, which cop- 
ulates in the fall of the year, the spermatozoa remain 
active during the entire winter and fecundate the 
ovum, which is discharged only in the spring. The 
number of spermatozoa in one ejaculation has been 
estimated to be upward of two hundred and twenty-five 
millions, and eight hundred and forty-eight millions are 
said to be formed for one Graafian follicle (Lode). “ The 
whole of the spermatozoa derived from a spermatophore 
(spermatocyst) are together equal to one ovum.”2 
Spermatogenesis.—The walls of the tubuli seminif- 
eri, cylindrical tubes forming the glandular substance 
of the testes, consist of two layers,—an external, or 
tunica propria, and an internal, or lining epithelium. 
The lumen is relatively large and tlie walls strong. 
The diameter of the tube is from to inch 
(Quain). The length of each tube is about two feet, 
and between eight hundred and nine hundred tubes 
have been found in a single testis. The epithelial lin- 
ing of the duct (seminal cells) consists of an outer 
layer near the tunica propria and an inner layer of 
1 Bossi, Nouvelles archives d’obstetrique et gynecologic, April, 1891. 
2 Balfour, Comparative Embryology, vol. i, p. 54. THE SPERMATOZOON; SPERMATOGENESIS. 
small granular cells. Between these is a layer of so- 
called supporting tissue,—Sertoli’s columns (Minot). 
From the small cells are developed the spermatozoa. 
A large cell nearest to the tunica, the parent-cell, 
divides into two or three mother-cells, and these again 
divide into daughter-cells, which lie nearest to the semi- 
niferous duct. The cells of this column are called 
spermatocysts. From the daughter-cells are formed 
the spermatoblasts, the last stage in the development 
of the spermatozoa. The head of the spermatozoa is 
largely formed from the chromatin of the nucleus, the 
middle piece within the nuclear membrane; while the 
Fig. 18. 
tail, or contractile thread, arises from the protoplasm 
at a later period. The cell-membrane finally disap- 
pears, and a column of material filled with nuclei, its 
lower end resting on a single large cell (parent-cell), is 
left.1 The spermatozoa attached to the upper (inner) 
end of the column are ultimately set free into the semi- 
niferous canal, the column subsequently disappearing, 
—according to some, by a process of fatty degeneration. 
The Ovum,—The fully-cleveloped human ovum is a 
clear, spherical body, measuring, with its envelopes, 
about inch in diameter. It consists of five por- 
1 The latest and most satisfactory account of spermatogenesis is to be 
found in Minot’s treatise, p. 42. HUMAN EMBRYOLOGY. 
tions,—an external membrane, an internal membrane, a 
yelk, a nucleus, and a nucleolus. 
The Zona pellucida, external membrane, so called 
from its transparent appearance, is developed from the 
primary Graafian follicle. It is a rather thick and 
Fig. 19. 
tough membrane, and appears striated from the pres- 
ence of minute pore-canals, the purpose of which is not 
distinctly understood. In man the Zona pellucida has 
a diameter of about 20 p (Minot). 
The Vitelline membrane, internal membrane, a very 
thin and delicate covering, is developed from the egg 
itself, and lies in close contact with the yelk. Between 
the two envelopes a slight space, the peri-vitelline space, 
exists, so that the egg moves freely within the Zona 
pellucida. 
The Yelk, or Vitellus, is somewhat granular in ap- 
pearance, and is composed chiefly of yelk-grains—the 
nature of which is not determined—and protoplasm. THE SPERMATOZOON ; SPERMATOGENESIS. 
29 
The amount of yelk in the human ovum is small, there 
being no necessity for a reserve supply after the ovum 
has escaped into the Fallopian tube, where, during its 
migration, it is nourished by the transudation of the 
secretion from the tube. 
The Nucleus, Germinal vesicle, vesicle of Purkinje, 
occupies an eccentric position in the ovum, and is sur- 
rounded by a nuclear membrane. Its interior is trav- 
ersed by a net-work of threads (chromatin), which ra- 
diate from the nucleolus; the interstices are filled with 
an albuminoid material called deutoplasm (achromatin). 
The Nucleolus, Germinal spot, spot of Wagner, con- 
sists mainly of chromatin,1 and is placed somewhat 
eccentrically in the nucleus. 
Maturation of the Ovum.—The process by which the 
ovum becomes fully ripe and ready for impregnation is 
known as maturation. The first stage consists in the 
Fig. 20. 
approach of the nucleus to one pole of the ovum (ani- 
mal pole) and a shrinking of the yelk, so that a space 
filled with clear fluid exists between the Yitelline mem- 
brane and the Zona pellucida. The nucleus then be- 
comes pale and its membrane disappears, the nuclear 
1 So called from its strong affinity for staining fluids. Acliromatin 
exhibits just the opposite condition. 30 
HUMAN EMBRYOLOGY. 
substance lying free in the yelk. Fine, thread-like, par- 
allel strands then appear and unite at their top and bot- 
tom to form a spindle-shaped body. At either end of 
this the clear protoplasm of the surrounding material 
becomes arranged in rays, producing a sun-like appear- 
ance,—archiamphiaster. The chromatin of the nucleus 
occupies a central position in this spindle body, and 
shows like a darkish band across the latter. The spin- 
dle then advances toward the surface of the egg, push- 
ing before it some of the yelk-substance until a rounded 
mass containing a portion of the former is projected 
between the egg and the Zona pellucida. This body 
becomes constricted off and forms the First Polar Globule. 
A second nuclear spindle is then formed from the rem- 
nants of the first still in the egg, and a Second Polar 
Globule is extruded as described. The remaining por- 
tion of the spindle subsequently re-appears as a nucleus 
in the egg, but is much smaller than the original ger- 
minal vesicle. It is now called the Female Pronucleus. 
It is estimated that about three-fourths of the original 
spindle is cast off in the polar bodies. The formation 
of these globules may take place either in the Graafian 
follicle or after the ovum has entered the tube; their 
fate is uncertain. The purpose of the polar globules 
has given rise to much discussion. It has been sug- 
gested that these cells are removed to make room for 
the male element necessary to fecundation ; that by this 
process parthenogenesis is prevented,1 etc. It has been 
shown that in the self-fertilized summer eggs of the 
maple-leaf louse, and other insects, but one polar glob- 
ule is formed ; while in the winter eggs, which require 
the addition of the male element, two globules are 
thrown off.2 
1 Balfour, Comp. Embryology, vol. i, pp. 62 and 63. 3 Blochmann. THE SPERMATOZOON ; SPERMATOGENESIS. 
31 
Ovulation consists in the rupture of a Graafian fol- 
licle and escape of the ovum. The causes which act to 
produce this are not known; by some ovulation is con- 
sidered synonymous with menstruation. While the 
ovum is developing, changes also take place in the 
Graafian follicle; it becomes more and more distended 
with fluid, and its walls are thinned, especially at one 
point,—the Stigma, the point of rupture,—so that it 
finally projects as a clear vesicle on the surface of the 
ovary. Rupture having taken place, the ovum, sur- 
rounded by the discus proligerus, either enters the 
Fallopian tube and begins its journey to the uterus, 
or falls into the peritoneal cavity and perishes. It is 
altogether probable that ovulation may occur prior to 
puberty and continue after the establishment of the 
menopause, and it is well established that it does take 
place during the intermenstrual period. 
Changes in the Graajian Follicle After Rupture.— 
These depend somewhat on the time of month at which 
ovulation occurs. The discharge of the ovum and the 
emptying of the fluid contents of the follicle are fol- 
lowed by the formation of the Corpus luteum. 
Corpus Luteum of Menstruation (False Corpus Lu- 
teum).—The bursting of the distended vesicle relieves 
the pressure on the surrounding blood-vessels, which at 
this period are greatly engorged, and gives rise to haem- 
orrhage into the collapsed follicle. This blood soon co- 
agulates, forming a firm clot within the cavity, but not 
attached to its walls,—the Corpus haemorrhagicus. Hy- 
pertrophy of the follicle-wall then takes place, as the 
result of which the wall is thrown into irregular folds, 
which encroach more and more upon the central clot. 
Contraction and diminution of the clot follow, while 
capillary loops, surrounded by newly-formed cells from 32 
HUMAN EMBRYOLOGY. 
the follicle-wall, penetrate its substance. In an external 
layer of cells around the clot pigment-granules of lutein 
are formed, and give rise to the yellow margin from 
which the corpus derives its name. The point of rupt- 
ure in the follicle is marked by a fine stellate line. After 
the third week changes of a retrograde nature begin in 
the corpus luteum, and ‘‘ at the end of eight or nine 
weeks the whole mass is reduced to the condition of an 
insignificant, yellowish, cicatrix-like spot.”1 A period 
of seven or eight months, however, may elapse before 
this spot has entirely disappeared. When the Graafian 
follicle ruptures during the intermenstrual period, little 
or no haemorrhage may result, the vesicle-cavity being 
filled by a whitish coagulum, the origin of which is 
unknown.2 
Corpus Luteum of Pregnancy ( True Corpus Luteum). 
—The intervention of pregnancy produces a very re- 
markable change in the behavior of the corpus luteum. 
Instead of diminishing in size, it continues to enlarge 
up to the fourth month, the walls becoming thicker and 
the convolutions more numerous. From the fourth to 
the seventh month of pregnancy it remains stationary 
and then gradually declines, so that at term it is much 
smaller than at the fourth month. The retrograde 
changes following labor are rapid ; by the eighth or 
ninth week post-partum the remains have become almost 
unrecognizable. 
Migration of the Ovum.—The assumed function of 
the infundibulum, in grasping the ovary just preceding 
the rupture of a Graafian follicle, must be considered as 
entirely chimerical. In all probability a large number 
of ova fall into the peritoneal cavity and become ab- 
1 Dalton, Human Physiology, 1875, p. 713. 
2 Coste. See also Leopold, Archiv fur Gynaltologie, Bd. xxi, p. 347. THE SPERMATOZOON ; SPERMATOGENESIS. 
33 
sorbed. Others are carried into the abdominal opening 
of the tube by a current produced by the ciliated epi- 
thelium of the latter, and from thence onward by the 
action of the cilia and the muscular contractions of the 
tube itself (peristalsis). That the cilia have much to 
do with the movement of the ovum is evident from the 
fact that women whose tubes have been deprived of 
their normal mucous covering by disease are usually 
sterile. In batrachians, in which the tubes are fixed, 
pathways of ciliated epithelium converging toward the 
openings of the tubes are formed on the peritoneum.1 
In cases of pregnancy where the corpus luteum is found 
on the side of a completely-occluded tube, it must be 
assumed that the ovum passed entirely around the 
uterus and entered the tube of the opposite side. Va- 
rious explanations have been ventured for this phenom- 
enon. It is supposed that a period of from six to eight 
days is consumed in the migration of the ovum from 
ovary to uterus. 
Impregnation.—Two varieties are considered, viz.: 
external, as in the osseous fishes, etc., in which the 
sperm is cast on to the ovum after it has left the body ; 
internal, as in mammals, in which the seminal fluid is 
deposited in the vagina or uterus during coitus. Im- 
pregnation of the ovum takes place in the outer third 
of the tube; an ovum which has reached the uterus 
without coming in contact with spermatozoa is no 
longer capable of fecundation (Bonnet). 
The manner in which spermatozoa obtain entrance 
into the uterus, traverse its cavity, aud enter the tube 
is not known. It is possible that, under the stimulus 
of copulation, an adspiratory process k set up in the 
1 Thiry, quoted by Lusk, Science and Art of Midwifery, 1884, p. 40. 
Heil, Archiv fiir Gyniikologie, Bd. xliii, p. 503. 34 
HUMAN EMBRYOLOGY. 
uterus, or that the retentive power of the abdomen con- 
tributes to the ascent of the spermatozoa.1 
A condition of attraction seems to exist between the 
egg and the spermatozoa ; the latter swarm about the 
ovum, attempting to penetrate its envelopes. Several 
may gain entrance through the Zona pellucida to the 
peri-vitelline space. As soon as the first spermatozoon 
approaches the yelk, a small protoplasmic swelling is 
thrown out toward the approaching organism. This 
may be penetrated by the spermatozoon, or, before this 
occurs, the projection may be withdrawn, leaving a slight 
Fig. 21. 
hollow or depression at its apex, through which the sper- 
matozoon enters. One spermatozoon only penetrates 
into the yelk, the resulting changes in some manner pre- 
venting ingress to the others. It has been suggested 
that the attractive power of the ovum is diminished or 
stopped by the entrance of the single individual (Minot). 
The spermatozoon, after entering the yelk, speedily 
loses its tail and middle piece, and the head enlarges by 
absorption from the surrounding material. The head 
has now become the Male Pronucleus. Around each 
pronucleus a clear spot is formed, and from this the 
protoplasm soon radiates in tine lines, forming an aster. 
1 Duncan, Researches in Obstetrics, p. 431. THE SPERMATOZOON ; SPERMATOGENESIS. 
35 
Each nucleus now approaches the other and also travels 
toward the centre of the egg. Meeting, they remain in 
contact for a time, and then fuse,—probably by a solu- 
tion of their wall-membranes,—and together form the 
First Segmentation Nucleus. The whole ovum is now 
called the Oosperm.1 The process of impregnation has 
been chiefly studied in the lower animals, those having 
a transparent ovum being selected for this purpose. 
According to Bonnet, in the sea-urchin the entire process 
occupies but ten minutes. 
Menstruation.—Every healthy, normally-developed 
woman, between the age of puberty and the menopause, 
has a discharge of blood from the uterus, lasting on the 
average about five days, and recurring periodically, ex- 
cept during pregnancy, once every twenty-eight or 
thirty days. The menstrual discharge is acid, non- 
coagulable, of a peculiar penetrating odor, purplish-red 
(prune-juice) color, and consists of blood, uterine and 
vaginal secretions, white blood-corpuscles, and epithelial 
scales.2 The amount lost during a period is variously 
estimated from 100 to 200 grammes (Lantois). The 
flow from the genitals is usually associated with more or 
less local and often general disturbance, especially of a 
secondary or reflex nature. The process primarily con- 
cerns the uterus, but it is possible that the tubes may 
also participate in the condition (Tait). Menstruation 
is the sign of perfected womanhood. The changes which 
take place in the uterus during the period consist in the 
destruction of its superficial mucosa, the, exposure and 
rupture of the capillaries, followed by a development of 
new cells and restoration of the lining membrane. 
1 Balfour, Comparative Embryology, p. 66. 
2 Krieger, Die Menstruation, Berlin, 1869. SECTION IV. 
The General Development of the Embryo. 
Segmentation.—Following the formation of the first 
segmentation nucleus, a short resting stage occurs, and 
then begins the active division of the yelk,—segmenta- 
tion. The pronucleus undergoes karyokinesis, or indi- 
rect cell-division, and then a groove appears around the 
oosperm, at right angles to the position assumed by the 
dividing nucleus. This primary groove passes through 
the axis of the oosperm, its position being marked by 
the two polar globules. The groove, deepening, divides 
Fig. 22. 
the oosperm into two parts. A second groove at right 
angles to the first then appears, and four cells result. 
The third groove, at right angles to the first and second, 
divides the four cells into eight, and segmentation con- 
tinues in a somewhat irregular manner until the oosperm 
assumes a form which has been compared to a mulberry, 
and is called the Morula, each cell of which contains a 
nucleus. 
In those eggs (e.g., fowl) in which the process of de- 
velopment goes on outside the body, the segmentation 
is only partial, and is known as meroblastic segmentation, 
the greater portion of the yelk being reserved for the 37 
GENERAL DEVELOPMENT OF THE EMBRYO. 
nourishment of the embryo. When the embryo is 
nourished inside the maternal organism (e.g., mammals), 
the segmentation is total, or holoblastic. The oosperm 
has by this time reached the uterine cavity. Here it 
gradually enlarges, a cleft filled with clear fluid makes 
its appearance in the interior of the solid mulberry 
mass, and a cavity is formed,—the Segmentation Cavity. 
The oosperm has now dilated into a vesicle, and is known 
as the Blastodermic Vesicle, or Blastula, the walls of 
Fig. 23. 
which, formed of a double layer of cells, is the Blasto- 
dermic Membrane. The cells of the interior of the mul- 
berry mass are crowded together at one point in the 
blastodermic vesicle, forming a lens-like body. The 
former minute egg has now increased in size by the ab- 
sorption of fluids from the uterus so as to be visible to 
the naked eve. 
Development of the Three Primary Layers.— Covering 
Layer.—A section through the segmented oosperm at 38 
HUMAN EMBRYOLOGY. 
this period shows that part at which the lens-like mass 
is attached to be composed of three layers, the rest of 
the blastodermic wall having but two. The first of 
these three layers, the covering layer, extends com- 
pletely around the blastodermic vesicle, and is com- 
posed of a single layer of thin cells. It lies immedi- 
under the Zona pellucida, which by this time has 
become reduced to a thin membrane. The covering 
layer is a temporary structure, and either entirely dis- 
appears or unites with the layer immediately beneath. 
Fig. 24. 
The Ectoderm.—This hiyrer of single cells also ex- 
tends entirely around the blastodermic vesicle, lining 
the covering layer. 
The Entoderm.—The third or innermost layer, the 
entoderm, consists at first of the cells which form the 
lenticular body, but which at a later period grow by 
peripheral extension so as to line the ectoderm. 
The Mesoderm.—After a time a third layer of cells 
is developed between the two primary layers, and ex- 
tends from the axial line outward. This layer does not 
grow entirely around the blastodermic vesicle, like the 
others, but remains confined to that portion in which 
the developing embryo is situated. The origin of the 
mesoderm is still in dispute, but it is known that, when 39 
GENERAL DEVELOPMENT OF THE EMBRYO. 
once started, it becomes independent of the other two 
layers, and grows by the proliferation of its own cells. 
The mesoderm at first extends from just outside the 
Fig. 25. 
germinal area posteriorly to a short distance be}rond the 
primitive streak anteriorly. It grows in all directions, 
but as it extends cephalward it sends out two projec- 
tions, which, leaving an interval between them, unite 
and again spread out. A space is thus left just in 
front of the head in which two layers only exist,—the 
ectoderm and the entoderm. This space is the Proam- 
nion, the importance of which will be noticed farther on. 
Fig. 26. 
Two cavities of considerable size soon form in the 
mesoderm, one on either side of the mesian axial line, 
and these, gradually extending, split the middle layer 40 
HUMAN EMBRYOLOGY. 
into two leaves. The upper leaf goes with the ectoderm 
to form the Somatopleure, or beginning body-wall, while 
the lower leaf, together with the entoderm, forms the 
Splanchnopleure, or wall of the primitive digestive tract. 
The space between these two is the Ccelum, or primitive 
body-cavity. 
From these three primary layers of the blastoderm 
all the organs and tissues of the body are developed :— 
From the Ectoderm: The skin and its glandular 
structures, the mammary glands, hair, nails ; the cerebro- 
spinal system and nerves; the organs of special sense. 
From the Mesoderm: The chorium, muscles, bones, 
connective tissue, digestive tract, blood-glands, vessels, 
blood, lymphatics, spleen, urogenital apparatus. 
From the Entoderm: The epithelium of the digestive 
tract. 
Embryonic Area (Germinal Area).—As the result 
of the thickening of the blastodermic wall at the point 
where the three layers exist, a distinct patch is seen 
when the oosperm is viewed from above. This is the 
embryonic area, in the central long axis of which the 
embryo is developed. At first the area is oval or 
shield-shaped, but during the formation of the prim- 
itive streak it enlarges, and one end becomes drawn out 
so that at that time it resembles a pear. (See Fig. 25.) 
Primitive Streak.—At a point in the median axial 
line of the germinal area, a little posterior to the centre, 
a thickening of the cells of the ectoderm takes place, 
and gradually includes the other two blastodermic 
layers, so as to form a distinct spot. This is the Knot 
of Hensen,—the anterior boundary of the primitive 
streak,—the latter being a continuation of the thick- 
ened wall, extending backward toward the margin of the 
germinal area. (See Fig. 25.) UENERAL DEVELOPMENT OF THE EMBRYO. 
41 
Medullary Plate and Groove.—The Ectoderm in front 
of the primitive streak, on either side of the median 
line, increases in thickness by a proliferation of its cells, 
so that a band of cells several rows deep results. This 
forms the Medullary Plate. The edges of the plate on 
either side and at the cephalic end of the shield then 
grow upward from the surface of the shield,—Medullary 
Folds, —thus forming a deepening groove between their 
sides,—the Medullary Groove. The lower portion of 
this groove is shallower than the upper end, and appears 
to embrace the beginning of the primitive groove. The 
sides of the groove continue to rise higher and higher, 
Fig. 27. 
at the same time arching inward so that after a time 
they meet in the central line, their edges fuse, and a 
tube is formed,—the Medullary or Neural Canal. This 
canal first closes in the future cervical region and after- 
ward at the head end, the posterior portion remaining 
open for a time as the Sinus Bhomboidalis. The medul- 
lary canal is the primitive central nervous system. It 
is now easily understood how the external layer of the 
blastoderm comes to form the brain and spinal cord. 
The Notochord.—Just below the medullary groove a 
rod of cells, beginning at the future Pituitary Body and 
running to the primitive streak, is developed from the 42 
HUMAN EMBRYOLOGY. 
entoderm. This is the Notochord, the first indication 
of the future skeleton. After a time the notochord 
becomes separated off' from the entoderm, which grows 
under its lower surface. (See Fig. 28.) Above, as the 
medullary groove deepens, the notochord comes to lie 
directly below the canal, but it does not unite with it. 
The notochord is a temporary structure, and commences 
to disappear during the second month of embiyonal life 
(Minot). 
Protovertebrae.—At the time that the notochord is 
forming a longitudinal thickening of the dorsal meso- 
derm takes place on either side of the chord. Two 
Fig. 28. 
lateral plates result. (See Fig. 29.) That portion nearest 
the chord is thickest, the plate gradually thinning out 
toward the blastodermic wall. The thicker portion is 
divided from the thinner, and is called the Segmental 
Zone, while the thinner portion is the Parietal Zone. By 
a process of transverse cleavage of the segmental zone a 
series of squarish bodies, or somites (Balfour), is formed. 
These bodies are afterward converted into cavities. 
They bear a certain relation to the future vertebrae, as 
well as to the muscular and dermal development. 
Folding off of the Embryo.—Tlie germinal area alone 
has to do with the development of the embryo, the rest GENERAL DEVELOPMENT OF THE EMBRYO. 
43 
of the blastodermic vesicle merely furnishing nutriment 
while the various processes are going on, the wall acting 
fig. 29. 
as a support. Up to this time the embryo lies flat upon 
the surface of the vesicle. Now a constricting fold 
Fig 30. 
appears around the embryo, slightly raising it above the 
rest of the blastoderm. This fold is more marked anteri- 44 
HUMAN EMBRYOLOGY. 
orly, where it is called the Head-fold, and posteriorly, 
where it is known as the Tail-fold. At the sides it is 
at first not quite so deep.1 The anterior or cephalic 
end of the embryo now appears to be slightly raised 
above the surface of the blastoderm, and at the same 
time to sink downward into the vesicle, an explanation 
of which will be seen in the next chapter. As the result 
of the deepening of the head-fold a cavit}r is shut off 
just below the notochord. This cavity is the Foregut, 
or the beginning of the alimentary canal. A similar 
cavity is also formed behind, and is called the Hindgut. 
At the sides, where the folds are not so deep, the 
opening into the vesicle is still wide. The yelk-sac, 
now called the Umbilical Vesicle, has already begun to 
diminish in size, and is connected to the embryo by a 
wide duct,—the Omphalo-mesenteric or Vitelline Duct. 
1 These are not folds in the actual meaning of the word, as they 
result from the growth (enlargement) of the embryo. SECTION Y. 
The Uterine and Foetal Membranes; tiie Placenta 
AND UTERO-PLACENTAL CIRCULATION. 
The Deciduae.—Coincident with the impregnation 
of the ovum, active changes are inaugurated in the 
Fig. 31. 
uterus ; the organ becomes more vascular, increases in 
size, and its mucosa undergoes marked alterations. The 
mucous membrane of the body-cavity becomes greatly 
thickened, except at the openings of the os internum 46 
HUMAN EMBRYOLOGY. 
and the Fallopian tubes, where it remains thin and is 
thrown into folds. This lining is the Decidua Vera. 
When the oosperm has completed its journey through 
the tube and enters the uterus, it lodges in a depression 
between two of the folds of the vera, and these, grow- 
ing over it, soon shut it off from the general uterine 
cavity. The oosperm appears as if in a sac. These 
encapsuling folds form the Decidua llejlexa. 
As the embryo enlarges the reflexa also grows, and 
finally comes in contact with the decidua vera. The 
decidua reflexa is not a permanent structure, for, having 
served its purpose, it undergoes hyaline degeneration, 
Fig. 32. 
and by the sixth or seventh month of embryonal life has 
entirely disappeared. That part of the decidua upon 
which the oosperm rests, and from which the placenta 
will subsequently be developed, is the Decidua Serotina. 
The Chorion.—When the blastodermic vesicle has 
reached the uterus, and perhaps before, all of that por- 
tion of the somatopleure which is not concerned in the 
formation of the embryo, and which at this time consti- 
tutes the external envelope of the oosperm, develops 
numerous villi on its surface, which give it a shaggy 
appearance. This is the Chorion, and the whole egg is 
sometimes spoken of as the Chorionic Vesicle. That THE UTERINE AND FCETAL MEMBRANES. 
47 
part of the embryonic shield which is free from chorion 
subsequently becomes covered as the result of the 
formation of the amnion. In the uterus the tips of the 
chorionic villi touch and slightly penetrate the deciduae. 
As development proceeds that portion of the chorion 
covered by the reflexa loses its villi and is called the 
Chorion Lseve, while that portion in contact with the 
serotina persists, enters into the formation of the pla- 
centa, and is called the Chorion Frondosum. 
The Amnion.—The description of the formation of 
the amnion usually given is that which takes place in 
the avarian and some mammalian embryos. In man 
Fig. 33. 
the process has been little studied, and appears to differ 
somewhat from that of other animals. 
Development of the Amnion in Ilen-Embryos.—At 
the same time that the so-called head and tail folds are 
forming, the upper leaf of the vesicle-membrane (soma- 
topleure), consisting of ectoderm and a part of the 
mesoderm, which was split off by the formation of the 
coelom, rises as a hollow ridge around the embryo, and, 
by a continuous growth upward and arching over the 
back of the latter, its edges finally meet and unite. 
Two layers are thus formed ; an internal, with the ecto- 
derm turned toward the embryo, and ail external, with 
the ectoderm turned toward the chorion. The upper 
and lower portions, respectively, of each layer consist 48 
HUMAN EMBRYOLOGY. 
of mesoderm. The internal layer has been called the 
true amnion, the external layer the false amnion. At 
first the amniotic membrane lies in contact with the 
dorsum of the embryo, but soon a clear fluid makes 
its appearance (the Amniotic fluid, Liquor amnii) and a 
cavity is formed (Amniotic cavity), which increases in 
size as the embryo develops. The space between the 
false and true amnions is in direct communication with 
the body-cavity. Some time during the third month the 
amnion comes in contact with the chorion and a loose 
connection between the mesodermic layers is established. 
This union never becomes firm, and the amnion can 
easily be stripped from the external membrane after 
delivery. 
Development of the Amnion in Human Embryos.— 
After the sinking of the embryo (see p. 44) a semi- 
circular fold of the vesicle-wall arises in front of the 
head and gradually grows upward and dorsal ward over 
the head and trunk of the embryo to the stalk of the 
allantois. The side portions of the fold unite over the 
embryonal anlage and grow in a longitudinal direction. 
The embryo thus becomes inclosed in the amniotic sac,1 
and is shut off from the chorion except at its posterior 
end, which forms the Bauchstiel. 
The Liquor Amnii.—This is a clear, watery fluid, 
having a specific gravity of 1007 to 1028, alkaline in 
reaction, and contains to 2 per cent, of fixed solids 
(Landois). Among these are albumin, urea, grape-sugar, 
chloride of sodium, and other salts. The liquor also 
contains epithelial scales from the skin, bladder, and kid- 
neys of the embryo, and lanugo,—wool-hair with which 
the embryo is covered. At term the amount of liquor 
is about a pound (15 to 18 ounces), but it is consider- 
' His, Anatomie Mensclilicher Embryonen, i, p. 172. THE UTERINE AND ECETAL MEMBRANES. 
49 
ably more than this near the middle of pregnancy. The 
liquor is derived from both the maternal and embryonal 
structures. During the later months of pregnancy the 
foetus adds to the liquor a considerable quantity of 
urine evacuated from the bladder.1 The liquor ainnii 
insures an equal distension of the uterus, protects the 
embryo from injury and the cord from pressure, facili- 
tates the dilatation of the maternal passages by “ the 
bag of waters ” during the first stage of labor, and lubri- 
cates the parturient canal during delivery. 
The Allantois.—In young embryos the allantois ap- 
pears as the continuation of the hind end of the body, 
Fig. 34. 
attaching the latter to the chorion in connection with 
the Bauchstiel.2 It arises as a hollow bud or diver- 
ticulum from the lower ventral surface of the hind- 
gut, and joins itself to the chorion to assist in the 
formation of the placenta. The allantois has a narrow 
canal in connection with the intestinal lumen. The 
lining is derived from the entoderm, while the outer wall 
is of mesoderm, derived from the intestine. The allan- 
* Nagel, Arcliiv fur Gynakologie, Bd. xxxv, p. 131. 
a The description of the Allantois, as given in most books, is that of 
the avarian or mammalian ovum. An allantoic vesicle is not found in 
the human embryo. See Hertwig, Kolliker, or Minot. 50 
HUMAN EMBRYOLOGY. 
tois carries with it from embryo to chorion two arteries 
and two veins. 
The Placenta. — This is the organ of respiration 
(sometimes called the foetal lung) and nutrition of the 
foetus. At term the placenta is a softisli, spongy mass, 
usually covered more or less with blood, and varying in 
color from light to dark red. It is round, oval, or reni- 
form in shape, and presents two surfaces for examina- 
tion. The upper surface is irregular, rough, and trav- 
ersed by numerous furrows, which give it a somewhat 
checkered appearance. These patches are the cotyle- 
dons, between which the decidua (serotina) dips down, 
Fig. 35. 
forming partitions or septa. This upper surface of the 
placenta is that portion of the decidua which has split 
off from the uterine wall during the casting of the cake. 
The under, foetal surface of the afterbirth is smooth, 
concave, and glistening, and is covered bjT the amnion. 
Immediately under the latter membrane it is traversed 
by a net-work of blood-vessels, which appear distended 
and cord-like. The arteries lie external to the veins, 
which are the larger. At term the placenta is from six 
to eight inches in diameter, and one-third to over an 
inch in thickness at its thickest part, gradually thinning 
toward the edge. Its weight is about sixteen ounces, 51 
THE PLACENTA AND ITS CIRCULATION. 
but varies somewhat with the size of the child. The in- 
sertion of the umbilical cord in the placenta is always 
eccentric (Minot). 
The Umbilical Cord.—The sides of the Bauchstiel 
grow downward and inward and finally unite along its 
ventral surface, forming a tube, which includes the stalk 
of the allantois. The cavity of the tube is directly con- 
tinuous with the coelomic cavity. While these changes 
are in progress, the amnion, which at first arises from 
the Bauchstiel, becomes separated from the latter up 
to the insertion of the chorion; so that the umbilical 
cord at term is never covered by the membrane, as 
generally stated (His). 
The cord carries one artery and two veins, which 
soon establish a circulation between the embryo and the 
chorion, later with the placenta. In the further develop- 
ment of the cord the cavity becomes obliterated and 
the allantois and yelk-stalk shrivel and nearly or quite 
disappear. At term the cord appears as a“ long, twisted 
rope of tissue” (Minot) covered by epithelium, which 
is continuous with that of the amnion, and contains a 
jelly-like matrix,—Wharton’s Jelly,—which surrounds 
the vessels. Wharton’s jelly contains mucin, branched 
corpuscles, lymphoid cells, and connective-tissue fibrils 
(Landois). The vessels run in a spiral course, usually 
from left to right. The usual length of the cord at term 
is from eighteen to twenty inches, but it may be much 
longer or shorter. 
The Utero-Placental Circulation.—This is a subject 
of much controversy, but may be briefly outlined as fol- 
lows : Prolongations arise from the decidua serotina, 
and between these the chorionic villi penetrate. The 
vessels of the decidual prolongations (arteries), running 
in a somewhat irregular manner with many corkscrew- 52 
HUMAN EMBRYOLOGY. 
like turns, become tuft-like as they approach the surface 
of the prolongations, and by a solution of continuity 
lose their coats, so that they open freely into the inter- 
villous spaces. The veins, on the other hand, open at 
the base of the prolongations and along the decidua of 
the intervillous spaces. The chorionic villi thus hang 
more or less free in a sinus, and are bathed in maternal 
blood. Each decidual prolongation has its own current 
region, the blood being poured out from the sides of the 
Fig. 36. 
former, and is carried off by the veins which lie below. 
The greater the distance from the decidual prominences, 
the slower the blood-stream, until at the greatest dis- 
tance a stasis occurs, with resulting fibrin deposit. The 
circular sinus at the edge of the placenta receives the 
blood from the lowest prolongations, but, as it appears 
often interrupted, it can have blit limited importance in 
carrying off the blood. The chorionic villi rarely, if 
ever, penetrate into the mouths of the arteries, but they 
do enter the veins, and often for a considerable distance.1 
1 Bumm, Archiv fur Gynakologie, Bd. xliii, p. 181. SECTION YI. 
The Development of Special Organs and Parts— 
the Heart, Blood-vessels, and Blood. 
The Heart.—When the coelom, or body-cavity, is 
formed by the splitting of the mesoderm into two parts, 
the low’er portion, with the entoderm, forms the intestinal 
plate (splanchnopleure). Before the infolding and ap- 
proach toward each other of the two intestinal plates 
begin, a small cavity in the mesodermal portion of each 
plate is formed in the midst of a number of isolated 
cells situated at some distance from the middle line 
of the embryo, and in the region of the future throat. 
Fig. 37. 
The mesodermal cells which bound this cavity undergo 
a change and become endothelial in character. These 
two cavities are the two halves of the primitive heart- 
cavity. As the infolding of the intestinal plate pro- 
gresses, the two halves of the heart are brought nearer 
and nearer together, and, following coalescence of the 
plates, unite in the median line, the thin partition-wall 
disappearing and a single cavity remaining. As the 
heart-cavity enlarges it pushes the surrounding tissues 
into the pleuro-peritoneal space, forming a noticeable 
projection on either side. The heart lies on the ventral 
side of the future throat, and at first is attached above 54 
HUMAN EMBRYOLOGY. 
and below by a dorsal and a ventral mesocardium. The 
ventral mesocardium finally disappears, as does also the 
middle portion of the dorsal mesocardium, and the heart 
is left projecting freely into the body-cavity. 
At this period the heart consists of a short tube 
Fig. 38. 
having an external (mesodermal) muscular coat and an 
internal endothelial lining, the two coats being at first 
separated by a considerable interval. As the head-fold 
deepens it crowds the heart backward so that it comes 
to lie under the midbrain ; at a later period the growth 
Fig. 39. 
Fig. 40. 
of the neck carries the heart still farther backward. In 
the rabbit traces of the heart are visible when five proto- 
vertebrae have developed. A slight dilatation of the 
upper end of the heart-tube now takes place, marking 
the future aortic bulb. SPECIAL ORGANS AND PARTS. 
55 
The lengthening of the cardiac tube in a confined 
space causes it to assume an S-shaped bend to the right, 
—that portion of the S to the right and in front repre- 
senting the future auricles; that toward the left and 
behind, the ventricles. A constriction, the Auricular 
Canal, then appears, separating auricle from ventricle. 
Septa subsequently develop, which divide the single ven- 
tricle into two parts, and later other septa divide the 
auricle, each auricle being in communication, through 
the Foramen ovale, with its fellow, and with the ventricle 
of the same side. 
Blood-vessels.—The primitive blood-vessels develop 
as a cord-like net-work in the mesoderm (splanchno- 
pleure) of the embryonic area. This net-work does not 
include the whole of the area, but that portion repre- 
sented by the Areas Opaca and Pellucida. It is bounded 
by a limiting vessel, the Sinus terminalis, which in man 
subsequently disappears. Yellowish-red masses are seen 
at intervals in the net-work, the cells of which develop 
haemoglobin. A “ liquid vacuolatiou ” then takes place in 
the cord-like net-work, and the cells from the islands sub- 
sequently become detached and circulate as free blood- 
corpuscles (Minot). The newly-formed blood-vessels 
send out prolongations which meet with others, and, 
uniting, form a series of branches and ramifications. A 
growth of the blood-vessels toward the embryo also 
takes place, the vessels penetrating to the heart, and 
thus the circulation is established. 
While the changes described are taking place in the 
heart, blood-vessels are also developing in various parts 
of the embryo, as described, and a primitive circulation 
is soon established. The tubular heart is continued 
THE PRIMARY EMBRYONIC CIRCULATION. 56 
anteriorly as a single vessel, the Truncus arteriosus. 
This divides in the region of the first branchial arch, 
each branch running right and left around the body- 
cavity to the posterior surface of the embryo, where 
they turn caudalward and extend in the long axis of the 
embryo to its hind end. These two vessels are the Primi- 
tive Aortae. Lateral branches are given off from the 
aortse, the largest of which are the Omphalo-mesenteric 
Arteries. 
HUMAN EMBRYOLOGY. 
The blood is returned to the heart by large veins in 
the area vasculosa. From the anterior portion of the 
Sinus terminalis it flows through the two Anterior Vitel- 
line Veins, which receive branches along their course; 
from the posterior portion of the sinus it returns 
through the Posterior Vitelline Veins. All of the veins 
unite near the middle of the embryo, in the Omphalo- 
mesenteric Vein, which enters the posterior end of the 
heart-tube. 
SECONDARY EMBRYONIC CIRCULATION ; AORTIC ARCHES. 
At a later period than described above, a right and 
left arterial branch is given off from the Truncus arteri- 
osus at the first visceral arch. These run along the 
arches to the back of the embryo and unite on either 
side of the vertebral column with the Primitive Aortse. 
Four other pairs of these aortic arches follow in suc- 
cession and terminate in the same manner. 
From the internal portion of the first arch on either 
side are developed the External Carotid Arteries ; the 
third arch and the external (dorsal) parts of the second 
and first arches enter into the formation of the Internal 
Carotid Arteries. From the dorsal (external) portion 
of the fourth arch is given off the Vertebral Artery, and 
from this arises the Subclavian Artery; from the last SPECIAL ORGANS AND PARTS. 
57 
arch are given off the Pulmonary Arteries, which at first 
are connected with the Dorsal Aorta by the Ductus 
Botalli. 
The Iliac Arteries arise from the umbilical arteries 
as soon as the leg-buds appear. The venous blood is 
collected in the head by the two Jugular Veins, in the 
body by the two Cardinal Veins. These trunks unite in 
the cardiac region and form the Ductus Cuvieri, where 
they are joined by other veins, and enter the lower end 
of the heart as the Sinus venosus. 
Blood. — The primitive red blood-corpuscles arise 
from the cells of the cord-like net-work during the 
process of lumen-formation, and multiply by indirect 
division. At first they are pale, granular, contain a 
large nucleus, and are surrounded by a layer of proto- 
plasm. The earliest form is probably spherical or 
spheroidal, the characteristic mature shape being as- 
sumed later (Minot). The origin of the leucocytes, 
before the development of the lymphatic glands, is not 
definitely known. 
The Central Nervous System. 
The Spinal Cord.—Following the formation of the 
Medullary, or Neural canal, a transverse section of that 
portion which is to become the spinal cord appears of 
an oval shape, and presents a small, central lumen 
bounded by thick sides and thinner ends. In the further 
development of the cord the sides increase in thickness, 
by a proliferation of their cells, but the end pieces do 
not participate in this growth, the result being two 
thickened lateral halves, united above and below, at the 
bottom of more or less deep anterior and posterior 
grooves, by thin commissures. The sides at a later 
period give rise to the spinal nerves, and in time are 58 
HUMAN EM15RY0L0GY. 
converted into the Anterior, Lateral, and Posterior 
Columns of the cord. 
Up to the fourth month the growth of the cord con- 
forms to that of the vertebral column, and extends from 
the first cervical to the last coccygeal vertebra. From 
fig. 41. 
that time on the bony structures outgrow the nervous, 
so that the cord appears to be shortened and no longer 
fills the canal. The lower end of the cord does not enter 
into the ganglia and nerve-cell formation going on in 
the upper portion, but remains tube-like, the point of 
demarkation from the rest of the cord being indicated by 
a small, conical enlargement,—the Conus medullaris. 
As the result of the superior growth of the vertebral 
column and consequent apparent shortening of the cord, 
the terminal tube, which is attached to the coccyx, be- 
comes drawn out into a long, fine filament, which persists 
in adult life as the Filum internum and externum. 
Fig. 42. SPECIAL ORGANS AND TARTS. 
59 
At the beginning of the sixth month the conus is at 
the sacral canal, at birth it has reached the region of the 
third lumbar vertebra, and a year later it is at the lower 
border of the first lumbar vertebra, where it remains 
(0. Hertwig). 
Another result of the lengthening of the vertebral 
column is seen in the changed direction of the nerve- 
processes. At first the nerves spring from the cord at 
right angles, and so remain in the cervical region, pass- 
ing direct to the intervertebral foramina; but lower down 
their course becomes more and more oblique, until at 
the low'er end of the cord they run in a vertical direction 
and remain for some distance in the spinal canal before 
making their exit. This lower mass of nerves surrounds 
Fig. 4; 
the Filum terminale, and forms the so-called Cauda 
equina. 
Between the third and fourth months an enlargement 
of the cord takes place at the point where the nerves are 
given off to the upper and lower extremities. These 
thickenings persist, and are known as the cervical and 
lumbar enlargements. 
The gray matter of the cord is first developed ap- 
parently from without inward, and is followed by the 
formation of the white matter, which proceeds from a 
differentiation of the outermost layer of cells of the cord. 
The Brain.—The anterior portion of the neural canal 
is at first a simple tube, but it soon dilates, and, two 
lateral constrictions appearing, it becomes divided into 
three parts,—the Primary Cerebral Vesicles (Fig. 43). 60 
HUMAN EMBRYOLOGY. 
These communicate through their central canal. The 
first of these vesicles is known as the Forebrain, the 
second as the Midbrain, and the third as the Hindbrain. 
These vesicles occupy about one-half of the dorsal 
portion of the entire length of the embryo. 
Cerebral Flexures.—The cerebral end of the neural 
Fig. 44. 
tube is at first straight,—that is, parallel to the surface, 
—but at an early period, as the result of the unequal 
development of the various parts of the brain, three 
bends take place. The first of these flexures occurs in 
the region of the midbrain, the forebrain being thus 
thrown forward and downward so that it lies at a right 
Fig. 45. 
angle and later at an acute angle to the hindbrain. The 
midbrain is also carried upward to the top of the head. 
This is the Primary liead-bend. 
The second bend occurs at the junction of the hind- 
brain and the cord. This throws the whole head still 
farther ventral ward, so that the floors of the fore- and SPECIAL ORGANS AND PARTS. 
61 
hind- brains come to lie parallel. This is the Neck- 
bend. 
The third bend consists of the forward growth of 
the ventral side of the hindbrain, and is called the 
Varolian bend (Minot). 
The Forebrain.—At the same time that the cerebral 
vesieles are being marked out, the walls of the first 
vesicle grow outward, forming lateral pouches,—the 
Optic Vesicles. The forebrain continuing to grow for- 
ward and upward, the optic vesicles become constricted 
off from the former until they are connected only by a 
narrow stalk,—the anlage of the Optic Nerve. A for- 
ward and upward growth of the dorsal wall of the fore- 
brain soon takes place, and, becoming constricted off’, 
forms a fourth vesicle,—the Secondary or Permanent 
Forebrain. This is the anlage of the cerebral hemi- 
spheres; the opening between it and the primary vesicle 
is the Foramen of Monro. 
From this permanent forebrain are developed the 
Cerebral Lobes, Corpus Callosum, and the Fornix. 
From the primary forebrain arise the Optic Thala- 
mus, the structures of the floor of the Third Ventricle 
(Tractus Opticus, Chiasma, Tuber Cinereum, Infundib- 
ulum, Corpora Mammillaria), the Pineal Gland, the 
Posterior Commissure, and the epithelium of the Tela- 
choroidea Superior. 
The Midbrain.—The midbrain takes the least active 
part in the development of the cerebrum of the three 
original vesicles. The posterior wall thickens, and the 
opening into the forebrain remains large. As the result 
of the development of the other parts, which grow over 
it, the midbrain is crowded downward and backward, 
ultimately forming the Aqueduct of Sylvius. From its 
roof are developed the Corpora Quadrigemina. 62 
human embryology. 
The Hindbrain.—At the time of the development of 
the head-bend the length of the hindbrain more than 
equals that of the rest of the brain (Minot). The third 
vesicle is soon differentiated into two portions,—a dorsal 
part with thick walls, the anlage of the Cerebellum, and 
a ventral portion, the Varolian bend, the apex of which 
is the anlage of the Pons Varolii. 
That part of the thickened wall between the pons 
and the cord becomes the Medulla Oblongata. 
The ventricle of the third vesicle becomes the fourth 
ventricle of the adult brain. 
The Olfactory Lobes arise as a longitudinal ridge from 
the under surface of the primitive hemispheres during 
the fourth week. 
The Urinary Organs. 
The Kidneys.—The development of the kidneys takes 
place in three stages :— 
Fig. 46, 
1. A solid rod of cells, probably derived from the 
ectoderm, makes its appearance in the “ intermediate 
cell-mass ” lying between the protovertebrae and the 
point of junction of the body and intestinal plates 
(somatopleure and splanchnopleure). In the rabbit this 
rod appears between the eighth and ninth day, in the SPECIAL ORGANS AND PARTS. 
63 
region of the fourth or fifth protovertebra, and develops 
rapidly caudalward to the posterior end of the primitive 
gut. The rod soon acquires a lumen which opens into 
the dorsal side of the lower portion of the allantois, 
where that structure is given olf from the liindgut. 
The cells around the canal now develop, and a longi- 
tudinal column is formed, which projects somewhat into 
the coelom. This projection is called the Wolffian Ridge, 
while the canal is the Segmental or Wolffian Duct. This 
duct functionates as a ureter until the development of 
the permanent kidney. 
Fig. 47. 
2. Within the column a simple comb-like gland ap- 
pears. A series of lateral (transverse) tubules are de- 
veloped, which open into the duct (externally), a few 
of them also opening into the body-cavity (internally). 
The parts about the tubules and duct become more com- 
pact and vascular, and convoluted canals and glomeruli 
are developed. This gland is the Wolffian Body. All 
except the upper end of this body ultimately disappears 
(eighth week). 
3. Just above its opening into the Cloaca a tubular 
bud is developed from the dorsal side of the Wolffian 
duct. The upper part of this bud grows quite rapidly, 64 
HUMAN EMURYOLOUY. 
extending forward to the cephalic end of the Wolffian 
body, where it dilates and covers the latter dorsally. 
This is the anlage of the permanent kidney. The gland- 
ular parts of the kidney are subsequently developed from 
the surrounding cells. 
The forward growth of the blind end of the renal bud 
causes its lower portion to become more and more 
stretched out until a long, narrow tube is formed,—the 
Ureter. At first the ureter opens into the Wolffian 
duct, but as the result of subsequent changes it acquires 
Fig. 48. 
a separate opening into the Urogenital Sinus, in front of 
that of the Wolffian duct. 
The Supra-renal Capsules.—These capsules consist of 
two parts, which originate independently. The cortical 
portion of the capsule is derived from the mesoderm, 
while the medullary portion develops from an offshoot 
from the sympathetic nervous system, lying in the 
abdomen below the aorta. The two parts unite at an 
early age, forming a body which at first is greatly in 
excess of the kidney in size. 
The Bladder.—During the second month of embry- 
onal life that portion of the allantois which lies within 
the abdominal cavity, and which is still in open com- 
munication with the lower end of the intestine (Cloaca), SPECIAL 0RUANS AND PARTS. 
65 
becomes dilated into a spindle-shaped vesicle, the middle 
portion of which represents the future urinary bladder. 
The distal portion of the spindle is still pervious up to 
the umbilical opening, but its lumen gradually narrows, 
and in time the whole dwindles to a solid connective- 
tissue cord, the Urachus, extending from the summit of 
the bladder to the umbilicus, and forming the Ligamen- 
tum vesicae medium. The spindle-shape of the bladder 
Fig. 49. 
persists for a considerable time. The organ is lined by 
entoderm ; the connective tissue and muscle of the walls 
are derived from the mesoderm. 
The Urethra.—See under “ External Genitals.” 
The Alimentary Tract. 
The primitive gut is formed by the infolding and 
fusion of the splanchnopleural plates, and at first extends 
as a simple tube nearly the whole length of the embryo. 66 
HUMAN EMBUY0L0GY. 
It soon becomes differentiated into three parts,—the 
Foregut, that part lying within the head-fold, and from 
which are developed the pharynx, oesophagus, stomach, 
and duodenum; the Hindgut, that portion included 
within the tail-fold ; and the Midgut, lying between these 
two and opening on its ventral surface into the yelk- 
Fig. 50. 
sac. From the latter the large and small intestines are 
developed. 
The Mouth.—By the formation of the head-fold the 
ectoderm and entoderm of the primitive gut are brought 
together at a point between the forebrain and the 
heart. The mesoderm is pushed caudalward so that 
Fig. 51. 
the outer and inner layers of the blastoderm are in appo- 
sition. This point is called the Oral Plate. As the re- 
sult of the head-bend the oral plate is carried downward 
and to the ventral side of the head. Heart and fore- 
brain now growing forward, a pit is formed between the 
two, at the bottom of which lies the oral plate, the sides SPECIAL ORGANS AND PARTS. 
67 
being covered by the somatopleure, extending from 
heart to head. This pit appears about the twelfth day 
(His). Rupture of the oral plate now taking place, 
a communication is established with the anterior end 
of the foregut, the opening representing the Primitive 
Mouth. The mouth at this time appears bounded by 
five sides, each side being raised in a small prominence. 
The upper tubercle, which is unpaired, forms the 
superior border of the mouth and is developed from 
the forebrain. The superior paired tubercles, Maxillary 
Processes, have to do with the development of the 
Superior Maxilla, while the lower two tubercles become 
Fig. 52. 
the Mandibular Processes, and are a part of the first 
Branchial Arch which forms the Inferior Maxilla. 
The Pharynx.—The upper part of the foregut, into 
which the mouth opens, and which is to become the 
pharynx, is much wider than the succeeding part of the 
gut, and at first is of uniform diameter. Very soon 
the upper portion of this cavity dilates, while the lower 
part contracts, a triangular or fnnnel-sliaped space 
resulting. At the beginning of the third week, four 
paired pouches, the first beginning at about the level of 
the mouth, extend outward from the entoderm of the 
sides of the pharynx until they meet the ectoderm, with 68 
HUMAN EM15RY0L0GY. 
which they unite. These pouches are called the 
Branchial, Visceral, or Gill Clefts. In the lower verte- 
brates a rupture of the membrane of the clefts takes 
place, forming slit-like openings into the pharynx ; but 
in man no opening is formed, the membrane persisting. 
The tissue between the clefts, composed of the three 
primary layers, appears as tongue-like ridges, which 
project on the external (ectodermal) and internal (ento- 
dermal) surfaces of the pharynx. These ridges are the 
Branchial Arches, five in number, and in them run the 
vessels forming the Aortic Arches. From the first vis- 
ceral cleft are developed the Auditory Canals, and from 
the second the Tonsils. The entoderm of the remain- 
ing two clefts is concerned in the formation of the 
Thymus and Thyroid Glands. 
From the first branchial arch are developed the 
Inferior Maxilla and the Incus and Malleus of the ear. 
The second arch gives rise to part's of the Hyoid Bone, 
and the third to parts of the Hyoid and the Thyrohyoid 
Bones. 
The fourth and fifth arches have no particular sig- 
nificance. 
The Tongue and Epiglottis are developed from the 
floor of the pharynx. 
The (Esophagus.—The folding in of the splanchno- 
pleural plates gives rise to the formation of a straight 
tube running along a portion of the lower aspect of the 
embryo. This is the primitive intestine, or Archenteron. 
The anterior portion of the tube is called the Foregut. 
Immediately behind (caudalward) the pharynx the fore- 
gut narrows into a short tubular portion,—the (Esoph- 
agus. During the fourth and fifth weeks, as the embryo 
body and neck elongate, tlie gullet becomes larger and 
longer, but still remains a comparatively straight tube. SPECIAL ORGANS AND PARTS. 
69 
The Stomach.—The stomach is indicated earl}’ as a 
slight, spindle-shaped widening of the foregut between 
the oesophagus and the liver. By the fifth or sixth 
week a decided bulging of the posterior wall of the gut 
has taken place, while the anterior wall becomes some- 
what depressed. The greater and lesser curvatures of 
the stomach are thus marked out. The stomach still 
lies in the axis of the body, but it soon descends into 
the abdominal cavity, and at the same time rotates so 
that it comes to lie across the body-cavity, the larger 
Fig. 53. 
end being carried to the left, while the lesser or pyloric 
end is turned to the right. While the direction of the 
stomach is longitudinal it is attached along its whole 
posterior length by mesodermic tissue to the body-wall, 
but as soon as the change in position takes place this 
attachment becomes drawn out into a thin membrane,— 
the Mesentery. Following rotation, that portion of the 
mesentery which connected the posterior wall of the 
greater curvature to the body becomes stretched out 
and folded, and forms the anlage of the future Omentum. 
The Intestine.—This includes all of the primitive gut 70 
HUMAN EMBRYOLOGY. 
between the stomach and anus. While like the rest of 
the tube it is at first straight, it increases rapidly in 
length and diameter, and as a result of this growth is 
thrown into numerous coils, which lie toward the ven- 
tral side of the body. 
The Duodenum is formed by a loop immediately 
below the stomach. Lower down another loop is devel- 
oped, the Vitelline Loop, which at a later period extrudes 
some from the body, and is in connection with the yelk- 
sac. As soon as the cloacal space becomes divided into 
urogenital sinus and rectum, the latter increases in 
thickness and diameter, and the lower portion of the 
gut develops into the Colon. 
The Caecum arises as a pouch from the vitelline loop 
in the region of the opening of the 3relk-sac. The 
formation of the Anus is described under “ The Sexual 
Organs.” 
The Liver.—This arises early as a diverticulum from 
the ventral side of the duodenum, and is situated behind 
the heart. A second diverticulum is almost immedi- 
ately formed from the first, and the walls of both become 
greatly thickened. These are soon permeated by blood- 
vessels; the cells between are converted into solid 
cords, which form a net-work, and later, acquiring a 
lumen, represent the lobular tissue and ducts of the 
liver. 
The duct connecting the liver with the intestine 
becomes the Common Bile-duct, and from this during 
the second month the Gall-bladder appears as a diver- 
ticulum. At birth the liver is very large, its weight to 
that of the whole foetus being as 1 to 18, while in the 
adult it is as 1 to 36 (Marshall). 
The Pancreas.—During the fourth week this develops 
as a bud from the dorsal portion of the foregut nearly 71 
SPECIAL ORGANS AND PARTS. 
opposite the liver, and grows dorsalward into the 
mesentery. Its duct is the remains of the original 
evagination. 
The Spleen.—This appears toward the end of the 
second month as an epithelial (mesenchymal) thicken- 
ing in the mesogastrium, in the vicinity of the pancreas, 
and close to the large blood-vessels. The collection of 
cells forming the spleen anlage become stratified, blood- 
vessels penetrate its substance, and the organ becomes 
gradually separated from the surrounding tissues, but 
still retains its connection with the mesogastrium. 
Fig. 54. 
The Lungs.—These begin about the fifteenth day as a 
vertical diverticulum (pulmonary anlage) of the ventral 
wall of the oesophagus, which extends from the fourth 
gill-cleft to the stomach. On transverse section at this 
time the oesophagus appears as an oval aperture, which 
lower down becomes pear-shaped. At the lower end 
the pulmonary groove divides into right and left pouches, 
which are surrounded by mesodermal tissue. A trans- 
verse section at this time shows the lumen of three 
tubes. These diverticula project into the body-cavity ; 
the peritoneum, which is pushed before them, forming 72 
HUMAN EMBRYOLOGY. 
the pleural covering and later the Pleural Sacs. By the 
growth and repeated branching of the lateral pouches 
the bronchi, bronchioles, and alveoli are formed, while 
the original tube, having separated off from the oesoph- 
agus, becomes the Trachea. The upper, slit-like opening 
into the pharynx represents the Glottis. 
The Larynx is developed during the fifth week as a 
dilatation of the anterior part of the trachea. 
The Sexual Organs. 
The External Genitals.—By the fourth week (Kolli- 
ker) an invagination of the ectoderm at a point on the 
posterior end of the embryo has taken place, so that 
this layer is brought in contact with the entoderm of 
the cloaca, and, rupture of the two layers following, an 
external opening is formed into the posterior end of the 
gut,—the Cloacal Opening, or Primitive Anus. 
A thickening of the anterior portion of the anal 
plate now takes place, giving rise to a slight protuber- 
ance, the Genital Eminence, which is the anlage of the 
Clitoris and Penis. On the under surface of the emi- 
nence a slight groove appears, the Genital Groove, and 
runs backward into the cloacal opening. The sides of 
this groove increase in size and project somewhat as 
the Genital Labia (Minot). About the middle of the 
third month a partition wall divides the cloacal space 
into two cavities, the anterior of which receives the 
urinary and Mullerian ducts, and is called the Urogenital 
Sinus, while the posterior opening persists as the Anus. 
The dilated portion of the arclienteron immediately 
above the anus, into which at first the allantois and 
intestine both open, is the Cloaca. 
By the further growth of this partition the two 
openings are carried farther and farther apart, the tissue SPECIAL ORGANS AND PARTS. 
73 
B 
A 
Male. 
Female. 
Male. 
Female. 
Fi©. 55. 74 
HUMAN EMBRYOLOGY. 
developing between them ultimately becoming the 
Perineum. 
Up to the fourth month the external genitals of the 
two sexes appear alike, but subsequent changes soon 
differentiate male from female. 
Male.—The genital eminence continues to elongate, 
and acquires a knob-like enlargement at its outer end,— 
the Penis and its Gians. As the result of this increase 
Fig. 56. 
in length of the eminence, the genital groove is also 
elongated and becomes deeper; at the same time the 
genital folds project farther, their edges meet, and, 
finally uniting, a long, narrow canal is formed, the male 
Urethra. This is continuous with the cloacal space, or 
urogenital sinus. The line of union of the genital 
folds is seen in the adult as the raphe of the penis. 
The Prostate Gland is formed by a circular thickening SPECIAL ORGANS AND PARTS. 
75 
in the walls of the upper end of the urogenital sinus. 
The glandular portion results from the ingrowth of the 
epithelium lining the canal. By the fusion of the lower 
portion of the ducts of Miiller the so-called Uterus 
masculinus, or prostatic vesicle, is formed. About the 
middle of the third month a slight prominence called 
the Genital Ridge develops on either side of the genital 
eminence. These ridges grow outward as folds, their 
edges meet and unite, and give rise to the future 
Scrotum,—the point of fusion of the folds persisting as 
the scrotal raphe. 
At a later period, preceded by the Processus vagi- 
nalis, the testicles descend and find lodgment in the 
scrotal sac. 
Female.—In the female the changes which take place 
in the formation of the external genitals are less pro- 
nounced. The genital eminence increases slowly in size 
and becomes the Clitoris, the genital folds enlarge and 
form the Labia Minora, and the sinus urogenitalis per- 
sists as the Vestibulum vaginae. Into this opens the 
Urethra—the elongated and narrowed portion of the 
allantois—and the vagina. 
The genital ridges enlarge b}r acquiring fat-tissue, 
project, but do not unite, and become the Labia Majora. 
The Prepuce of the clitoris is formed by the folds of 
skin which pass over the glans. 
INTERNAL ORGANS OF REPRODUCTION. 
Muller’s Duct.—At a period subsequent to the ap- 
pearance of the Wolffian duct, a second canal, the duct 
of Miiller, is developed external—that is, lateral—to the 
former. This begins as a thickening of the mesothe- 
lium of the Wolffian body, and extends backward as a 
solid cord to the allantoic portion of the cloaca. The HUMAN EMBRYOLOGY. 
anterior end of the cord becomes funnel shaped as the 
result of the invagination of the peritoneal epithelium, 
and the cord gradually acquires a lumen dorsalward. 
The duct of Muller, therefore, has two openings,—one 
above into the body-cavity, and one below into the 
allantois. In the female this duct is the anlage of the 
Fallopian Tube, the anterior opening representing the 
Morsus diaboli of the Odium abdominale, while the lower 
portion develops into the Utero-vaginal Canal. 
The Genital Fold.—At about the same time that the 
Fig. 57. 
development of the ducts of Muller takes place, a small 
ridge, the Genital Fold, is formed on either side, between 
the Wolffian body and the mesentery, and projects slightly 
into the body-cavity. This ridge extends nearly the 
whole length of the abdominal space, and is mainly 
formed by a thickening of the peritoneal epithelium, the 
Germinal Epithelium. The middle portion of this ridge 
is the anlage of the Sexual Gland. By further growth 
the genital fold becomes so intimately connected with 
the Wolffian bod}’ as to appear to have arisen from it. 
Further changes consist of the approach of the caudal SPECIAL ORGANS AND PARTS. 
ends of the urogenital ridges toward the middle line, 
where they unite to form the Genital Cord. 
The differentiation of sex in the internal organs 
becomes apparent about the fifth or sixth week. 
The Testis.—In that portion of the genital fold, the 
Sexual Gland, which is to become the testis, a series of 
cellular cords, Sexual Cords, are developed from the 
germinal epithelium. These are separated from one 
another by a loose, embryonal connective tissue. They 
contain a number of large nucleated cells,—the primitive 
Sperm Cells. The cords acquire a lumen and become 
the Seminal Canals. The anterior tubules of the Wolffian 
body extend into the sexual gland, unite with the semi- 
niferous tubules, and, anastomosing in various direc- 
tions, form the Rete testis; the outer portion of the 
tubules remaining as connecting channels—Vasa effer- 
entia—between the latter and the Wolffian duct. The 
anterior portion of the Wolffian duct becomes the 
Epididymis, the posterior part the Vas deferens. 
In the male the middle portion of the ducts of 
Miiller entirely disappears, the anterior part remaining 
as the Hydatids of Morgagni, while the posterior, the 
genital cord, becomes the Uterus masculinus. 
The Ovary.—In the development of the ovary the 
sexual cords, later called the Cords of PJluger, are 
larger than in the male, and the cells which the}" con- 
tain are much more numerous. The connection with 
the Wolffian duct is established in the same manner as 
in the male, the cords acquiring a lumen and becoming 
the tubuliferous tissue of the ovary. The large cells, 
which develop into ova, are derived from the germinal 
epithelium together with the cords. 
The upper portion of the ducts of Miiller become 
the Fallopian Tubes. 78 
HUMAN EMBRYOLOGY. 
The genital folds thin out into the Broad Ligaments. 
The tubules of the upper portion of the Wolffian 
duct persist as the Parovarium, with its longitudinal 
duct. 
The lower portion of the Wolffian duct persists, or 
not, in the genital cord as the Ducts of Gaertner. 
The Uterus and Vagina.—By the formation of the 
genital cord the two ducts of Muller are brought into 
apposition; their walls fuse, become thinner, and finalty 
disappear, leaving a single tube, or Genital Canal. 
A differentiation of this simple tube into uterus and 
vagina begins about the sixth month. (See Fig. 57.) 
The upper portion of the tube into which the Fallo- 
pian ducts open develops thick, muscular walls, repre- 
senting the Body and Fundus of the Womb, and a lower, 
knob-like prominence the Vaginal portion, or Cervix. 
In the lower portion of the tube the lumen remains 
wide and the walls thin,—the Vagina. 
With exception of the notochord (vertebra?), which 
is derived from the entoderm, all the bones of the body 
are developed from the mesoderm. In point of time 
the skeleton is relatively late in appearing, the anlage 
of most of the important structures of the embryo- 
body being already present before the future bony 
structure is indicated. The development of the skeleton 
may be placed in three stages : (1) the membranous 
stage; (2) the cartilaginous stage ; (3) the bony stage. 
The Skeleton. 
With certain exceptions, the bones of the body are 
first “ laid in ” in cartilage, which is later replaced by 
true bone,—the so-called cartilaginous ossification. A 
few bones originate in connective tissue, the process 
being known as intra-ligamentous ossification. SPECIAL ORGANS AND PARTS. 
79 
In both forms the process of ossification is essen- 
tially the same. 
The Muscular System. 
Following the division of the protovertebral plates 
of the mesoderm into the primitive segments, a differ- 
entiation of the cells of the latter bodies also takes 
place, two distinct portions being formed in each. The 
innermost of these parts, that which is nearest the me- 
dullary canal, is called the Myotome, while the outermost 
section is the Nephrotome. From the innermost portion 
of the myotome a body of cells is further differentiated, 
these cells being known as the Muscle-plate, and from 
which the muscular system of the body is developed. 
The muscle-plates grow rapidly, especially dorsalward, 
covering the medullary canal, and extending into the 
somatopleure. The muscles of the extremities are 
probably derived from offshoots from the muscle-plates. 
Development of the Extremities. 
The limbs appear in the thoracic and pelvic regions, 
as bud-like outgrowths of a lateral longitudinal ridge 
Fig. 58. 
which runs on the level of the lower end of the muscle- 
plates for nearly the whole length of the trunk (Bal- 
four). These buds are at first fiat and at right angles 
to the body. During the fifth week they have increased 80 
HUMAN EMBRYOLOGY. 
in size and divided into two parts, the distal and smaller 
segment being the future hand or foot. Notches also 
appear in the anterior margin of the hand, marking the 
future Fingers. During the sixth week a crease appears 
in the proximal portion of the limbs, which are thus 
divided into the Arm and Forearm, the Thigh and Leg. 
The Toes are also indicated at this time, and the limbs 
rotate so that the elbows point forward and the knees 
backward. By the seventh week the Nails appear as 
thickenings over the finger-tips ; their subsequent shift- 
ing to the dorsum of the lingers is the result of the 
growth of the palmar surface of the latter (Kolliker). 
The development of the anterior extremities is in ad- 
vance of that of the posterior. 
The Face. 
The development of the Mouth has already been 
described. (See page 66.) 
The Nose.—This develops at a very early age by the 
Fig. 59. 
thickening of a patch of ectoderm, the Olfactory Plates, 
on the under surface of the forebrain, in front of the 
mouth. An upgrowth of the ectoderm and mesoderm 
along the median, lateral, and superior borders of the 
plates soon converts them into depressions,—the Nasal SPECIAL ORGANS AND PARTS. 
81 
Pits (Fig. 60). The lower sides of these pits remain 
open, and by further growth a groove, the Nasal Groove, 
is formed, which runs backward to the mouth-cavity. A 
tongue of tissue, the Nasal Process, growing downward 
from the anterior wall of the head to the mouth, now 
sends out a rounded process, the Processus globularis, on 
either side; the two constrict the nasal openings, and, 
growing sideways, unite with the maxillary processes. 
The nasal grooves are thus covered in and two tubes 
formed, the posterior nasal passages, leading from the 
nasal pits to the cavity of the mouth. The epithelium of 
the plates gives rise to the olfactory or Schneiderian 
Membrane of the nose, and this at a later period is 
brought in relation with the Olfactory Lobes by means 
of ganglia developing in its epithelium. 
The middle portion of the nasal process, which 
appears depressed on account of the upgrowth of its 
sides, pushes forward, forming an angle at its lower 
middle end, and this becomes the tip of the future nose. 
The superior central portion of the process becomes the 
Nasal Bridge. 
By the growth of the surrounding parts the olfactory 
pits gradually become converted into the slit-like aper- 
tures of the Anterior Nares, while the Alae nasi are 
formed, toward the end of the second month, by the 
nasal ridges of the process. 
By the uniting of the two globular processes the 
anlage of the upper Lip is formed. Behind these a 
second ridge, arising, forms the anlage of the Gums. 
The Ear.—Internal Ear.—The first traces of the 
ear appear, about the fifteenth day, as a thickened plate 
of ectodermal cells, lying just back and above the first 
gill-cleft. An inpouching of the ectoderm here takes 
place, forming a pit, which is later covered over and 82 
HUMAN EMBRYOLOGY. 
separated from the tissues above as a vesicle,—the 
Auditory Vesicle, or Otocyst. The otocyst is at first 
round, but subsequently it sends out a dorsal prolonga- 
tion, the Recessus vestibuli, which later comes in contact 
with the Auditory Ganglion. 
Fig. 60. 
The Semicircular Canals and Cochlea are developed 
from the walls of the auditory vesicle. 
The Auditory Canal and Eustachian Tube arise from 
the first visceral cleft. 
Fig. 61. 
The Tympanum develops from the membrane cover- 
ing the first cleft. 
The External Ear.—During the first month six 
tubercles make their appearance around the end of the 
first branchial cleft,—two from the maxillary arch, three 83 
SPECIAL ORGANS AND PARTS. 
from the second arch, and one, intermediate, at the end 
of the cleft. A groove then appears below the tuber- 
cles on the second arch, raising the future Helix from 
the surrounding surface. The first tubercle of the max- 
illary arch becomes the Tragicum; the second and 
intermediate tubercles fuse to form, with the raised por- 
tion of the ear, the Helix; the first superior tubercle of 
the second arch becomes the Antihelix, the middle the 
Antitragus, and the last the Lobe. 
The Eye.—The development of the primary optic 
vesicles has already been described (page 61). 
The Lens.—By the fourth or fifth week a small pit, 
the Primary Optic Cup, is formed on the surface of the 
Fig. 62. 
Fig. 68. 
optic vesicle by the in pouching of the ectoderm. This 
cup increases in size, and is gradually constricted off to 
form a vesicle, the anterior portion of which is con- 
nected with the ectoderm for a time by a band of 
tissue. The vesicle is the future lens. As the con- 
stricting off of the lens progresses, the edges of the 
ectoderm approach each other and finally unite over the 
lens as an unbroken layer. At this point the ectoderm, 
together with the mesoderm, which grows in between 
the external layer and the lens, forms the anlage of the 
Cornea. 
The Retina.—As the lens develops the optic vesicle 
becomes invaginated behind it and forms a Secondary 84 
HUMAN EMBRYOLOGY. 
Optic Cup, which surrounds the lens on all sides except 
in front. The posterior wall of this cup ultimately 
unites with the posterior wall of the optic vesicle to 
form the retina, the original wall of the vesicle being the 
future Pigmented Layer. 
Between the lens and the retina there is at first but 
little space, but as the e}re enlarges this space is increased 
and furnishes the Vitreous Body. 
The secondary optic cup never entirely covering- 
over the anterior surface of the lens, a circular aperture 
is left, which forms the primitive Pupil. 
The Anterior Chamber of the e}Te is formed by a split 
in the mesoderm, which grows in between the ectoderm 
Fig. 64. 
and the lens, the external layer assisting in the forma- 
tion of the Cornea, the internal the Iris. The tissues 
about the eyeball become more compact and thicker, and 
form the anlage of the Sclera and the Choroid. 
The Optic Nerve.—At the same time that the invagi- 
nation of the optic cup takes place, a groove is formed 
along the lower border of the optic stalk. (See Fig. 64.) 
The lumen of the stalk is thus diminished, but an open 
communication still exists between the Third Ventricle 
of the brain and the Post-lenticular Space. The groove 
is called the Choroidal Fissure. An artery soon appears 
along this groove and runs through the vitreous 
to supply the lens,—the Arteria centralis retinae. The 
anterior part of the artery is subsequently obliterated. SPECIAL ORGANS AND PARTS. 
85 
The choroidal fissure suddenly closes up, from 
behind forward, and becomes a solid rod, which, acquir- 
ing nerve-fibres from the brain and retina, forms the 
optic nerve. 
The Eyelids.—These originate as upper and lower 
folds of integument in front of the eye. The folds 
increase in size, meet in the middle line and fuse, but 
again become separated before birth. SECTION VII. 
General Consideration of the Child at Birth. 
Owing to the arrangement of the circulation and 
the consequent better nourishment of the anterior por- 
tion of the body, the anterior part of the trunk and 
the head appear better developed at birth, but the 
increase in size thereafter goes on more rapidly in the 
lower extremities. The average weight of the child at 
birth is to 7T3ff pounds (Lusk), males being somewhat 
heavier than females.1 The average length of the infant 
is 20 to 21 inches. 
The Head is generally covered with hair about an 
inch long, and is usually misshapen as the result of 
pressure in the bony canal during labor, the so-called 
“ molding ” having effected a lapping of the bones 
along the line of the sutures. Furrows and depressions 
in one or more of the cranial bones may also be seen. 
A distinct swelling on that part of the head, face, or 
buttocks which presented at the uterine Os during labor 
may be present, and is called the Co,put succedaneum. 
This is a serous infiltration of the skin due to absence 
of pressure at that point during labor, with pressure on 
the surrounding parts. Cephalhsematoma, a circum- 
scribed haemorrhage situated between the pericranium 
and the bone, due to pressure or traumatism, is less 
frequently met with. Both swellings disappear,—the 
first in a few days, the latter in from ten to sixty days. 
* In 1000 cases noted by Parvin but one child weighed 11 pounds. In 
7000 cases LaChapelle found but 13 weighing 10 pounds, and none more. 
In 1156 cases Hirst records but one child of 12 pounds. Lusk saw one 
weighing 11 pounds in 200 cases. CHILD AT BIRTH. 
The last mentioned may go on to suppuration. The 
average size of the head of the newborn child immedi- 
ately after expulsion is as follows :— 
Bitemporal (BT) diameter, ... 8 centimetres. 
Biparietal (BP) diameter, . . . 9% “ 
Occipito-frontal (OF) diameter, . . 11% “ 
Occipito mental (OM) diameter, . . 13 “ 
Maximum (MM) diameter, . . . 13% “ 
Suboecipito-bregmatic (SOB) diameter, 9% “ 
Trachelo-bregmatie (TB) diameter, . 9%-10 “ 
Circumferences : OF, 34% cm.; SOB, 30 cm.; OM, 37 cm.1 
Circulation.—Marked changes take place in the cir- 
culation of the blood after birth. The foetus, which up 
to the time of delivery has been dependent upon the 
mother for aeration of the blood, nourishment, and the 
discharge of its elfete products, has now to carry on an 
independent existence. 
In the foetus the blood, returning from the placenta 
by the umbilical vein, divides into two currents,—one 
of which proceeds through the Ductus venosus to the 
Inferior vena cava, and thence to the Bight auricle of 
the heart; the other to the Liver through the Hepatic 
Veins and Arteries, and on to the Right auricle. When 
the heart contracts, the blood in the Bight auricle is 
forced through the Foramen of Botal into the Left 
auricle. The Right ventricle receives but a limited sup- 
ply of blood, a small part of which it sends to the lung 
through the Pulmonary artery, but most of which goes 
to the Aorta through the Ductus arteriosus. The Left 
ventricle receives the blood from the Left auricle and 
Pulmonary veins and sends it into the Aorta, where it 
mixes wdtli the blood coming from the Right ventricle 
through the Ductus arteriosus. The head and extremi- 
ties are supplied by the Aorta, and the blood is returned 
1 Hirst, Am. System of Obstetrics, vol. i, p. 215. 88 
HUMAN EMBRYOLOGY. 
to the placenta by the Umbilical vein. After birth ces- 
sation of the placental circulation and obliteration of 
the umbilical vessels take place. The Ductus venosus 
soon becomes transformed into a fibrous cord, the Fora- 
men ovale between the auricles is closed (in about fifteen 
days), and the Ductus arteriosus becomes obliterated. 
The circulation now assumes the character found in the 
adult. 
The Skin.—At birth this is of a rosy color, and is 
covered, on the back and flexor surfaces especially, by 
a whitish, sticky material,—the Vernix caseosa. This is 
composed of a greasy mixture of sebaceous matter and 
macerated cells and Lanugo, which by this time has 
nearly disappeared from the bod}’. The vernix contains 
47.5 per cent, of fat (Landois). 
The Breasts are well formed, the lobes are distinct, 
and the ducts open at the nipple. In both male and 
female children an enlargement of the gland often takes 
place, and a thin, watery, finally a milky, fluid may be 
squeezed out. 
Breathing.—As soon as the child is born the thorax 
expands, a few spasmodic inspirations take place, fol- 
lowed by more regular breathing and a more or less 
vigorous cry. The cause of the first inspiration has 
been variously stated, but it is probably due to the 
demand on the part of the system for oxygen. After 
the first inspiration the thorax never again assumes its 
previous form. 
The Nails of the fingers and toes are well formed, 
and those of the former project beyond the finger-tips. 
The Eyes are open and staring, but it is probable that 
no distinct perception of objects takes place before the 
fifth or sixth week. 
mtn or sixtn ween. 
The Testicles are usually down in male children ; the 
labia majora in apposition in females. CHILD AT BIRTH. 
89 
Excretions.—The urine of the newborn child is 
limpid, and after the first few hours abundant. It is 
sometimes stained with blood, bile, etc., and there may 
be at first a heavy deposit of sediment. 
The Meconium, a thick, tarry material resembling 
poppy-juice,—whence its name,—is passed in abundance 
from the bowel after the first few hours, but ceases, after 
a few days, to be present in the evacuations. It con- 
sists of water, mucus, epithelium, fat, cholesterin, and 
3 per cent, of bile-pigments, crystalline bilirubin, and 
biliverdin. 
EMBRYO AND F(ETUS AT DIFFERENT PERIODS OF 
DEVELOPMENT. 
First Month.—Indistinguishable from the ovum of 
other animals. Brachial plexus. Spinal canal closes. 
Buds of rudimentary extremities appear. Indication 
of eyes, anus, mouth. The heart is four-tenths inch 
long. 
Second Month.—About one inch long. The eyes, 
nose, and ears are distinguishable. Suggestion of hands 
and feet. External genitals. 
Third Month.—Ovum about the size of a goose-egg. 
Fingers and toes separated. Nails as fine membranes. 
Neck separates head from body. Sex distinguishable ; 
uterus formed. Weighs 460 grains. 
Fourth Month.—Six inches long. Weighs 850 grains. 
Lanugo present. 
Fifth Month.—Ten inches long. Weighs 8 ounces. 
Vernix caseosa forming. Eyelids begin to separate. 
Heart-sounds perceptible. Quickening takes place. 
Sixth Month.—Twelve inches long. Weighs 
ounces. Hair on head, eyebrows, and lashes. Testi- 
cles near rings. 90 
HUMAN EMBRYOLOGY. 
Seventh Month.—Fourteen inches long. Weighs 
ounces. Pupillary membrane disappears. 
Eighth Month.—Sixteen inches long. Weighs 
pounds. Left testicle descended. Nails do not pro- 
trude beyond finger-tips. Lanugo begins to disappear. 
Ninth Month.—Eighteen inches long. Weighs 
pounds. SECTION VIII. 
Changes in the Maternal Organism Incident to 
Pregnancy. 
The condition of pregnancy inaugurates a new era 
in the life of woman. Incident to this a great variety 
of changes take place in the maternal organism. Many 
of these are quite apparent, and are put down as the 
“ signs and symptoms ” of pregnancy, and serve to 
enable the physician to make a correct diagnosis of the 
gravid state; while others are more obscure, but not 
less important, a knowledge of which furnishes a key to 
many of the morbid processes which may arise during 
the pregnant state, at time of labor, or in puerpery. 
General Considerations.—The general appearance of 
the woman is changed. During thfe first few months 
mental or nervous manifestations and reflex phenomena 
are usually presented, nutrition is altered, every func- 
tion is augmented, “every drop of liquid, every cell, 
every fibre, every organ feels the new impulse.”1 
After the first few months, in the erect position the 
centre of gravity is shifted from an imaginary line run- 
ning from the top of the head through the ileo-femoral 
articulation and knee- and ankle- joints to a vertical line 
falling in front of the pubes. This is due to the for- 
ward growth of the uterus, and explains the squaring 
of the shoulders and tln*owing backward of the trunk 
seen in nearly all pregnant women.2 
1 Barnes’s Obstetric Med. and Surg., vol. i, p. 246. London, 1884. 
2 Duncan, Researches in Obstetrics, p. 38. London, 1868. 
The incurvation of the spine is increased and the 92 
HUMAN EMBRYOLOGY. 
pelvic inclination diminished. The nutrition is gener- 
ally augmented, fat accumulations sometimes taking 
place, especially in the abdominal parietes, and there 
is often a general rounding out of the body. An in- 
crease in weight of from 1.5 to 2.0 kilogrammes takes 
place during the latter months of pregnancy.1 
Owing to the changes in circulation, constitution of 
the blood, and consequent nutrition, softening of the 
pelvic joints takes place, and the osseous system as a 
whole is deprived to a greater or less extent of lime- 
salts, which are called off for the building up of the 
foetus. Fractures of the bones of pregnant women 
often heal slowly for this reason. 
Thin, bone-like masses, called osteophytes, consisting 
largely of lime-salts, are often deposited between the 
dura mater and the skull. They are supposed to repre- 
sent an excess of material prepared for the foetal bones, 
and may have some relation to the elaboration of milk. 
Owing to the intercalation of the placenta between the 
arteries and veins of the uterus, and perhaps partially 
as the result of the pressure of the enlarging organ 
upon the blood-vessels, a larger amount of work is 
thrown upon the heart, to meet which a compensatory 
hypertrophy of the left ventricle takes place. This 
gradually disappears after delivery, but following suc- 
cessive labors a slight subinvolution of the organ may 
persist. 
The Blood, as a whole, is increased in amount, espe- 
cially during the latter months of pregnancy, and is 
changed in the relative proportion of its constituents. 
The water, fibrin, and white corpuscles are increased, 
the red corpuscles diminished, and there is less iron. 
This may progress to such a degree as to give rise to a 
1 Gassner, Monatssclirift fiir Geburt. kunde, 1862. CHANGES IN THE MATERNAL ORGANISM. 
93 
physiological leucocytosis (Virchow), or even to a per- 
nicious anaemia. 
The excretions are generally increased, the glands 
of the skin and the kidneys becoming more active. The 
urine may contain normally a small amount of albumin, 
in from 3 to 5 per cent, of cases,1 and traces of sugar are 
often present. 
The Liver is sometimes enlarged as the result of a 
physiological fatty infiltration. 
The Lung-capacity, especially toward the close of 
pregnancy, is considerably diminished, respiration being 
accommodated by the spreading out of the thorax, the 
antero-posterior diameter being diminished. 
The Skin becomes more active, pigmented spots 
appearing at different points, notably on the face, abdo- 
men, and breasts. 
Special Considerations.—During gravidity the uterus 
enlarges from a small, hollow organ having a capacity 
of about 1 cubic inch,2 measuring about 3 inches in 
length by 2 inches in width at its widest part, and 
weighing from 7 to 12 drachms, to an immense sac 
occupying the greater part of the abdominal cavity, 
with a capacity of 400 cubic inches and a weight of 
about 2 pounds. This increase in size is gradual and 
dependent upon the influence exerted by the develop- 
ing ovum. The uterine wall is at first thickened, but 
afterward thinned, especially in its lower segment. 
The muscular fibres elongate and thicken until they 
ultimately become about eleven times as long and five 
times as thick as in the unimpregnated womb. At the 
same time there is an actual increase in the number of 
fibres (hyperplasia). 
* Veit, Muller’s Hamlbuch der Geburtshulfe, Bd. i, p. 224. 
s Simpson’s Works, 1871, p. 595. 94 
HUMAN EMBRYOLOGY. 
The Cervix uteri, with the exception of a slight thick- 
ening, does not participate in these changes, but remains 
practically the same until within a few weeks before 
delivery, when it is gradually taken up—i.e., shortened 
—and entirely disappears during the first stage of 
labor. 
The changes in the uterine mucosa have already been 
described in the discussion of the Deciduae. 
The other portions of the sexual organs are also 
more or less affected by the advent of pregnancy. The 
ligaments are stretched, but also increase in their tissue- 
elements. The ovaries are little or not at all affected. 
The Vagina is relaxed and moistened by secretions, 
the latter often amounting to a considerable discharge 
(lencorrhcea). The introitus vaginae presents a pale- 
violet or deep-purple tinge, the result of the retarded 
blood-flow. 
The External Genitals are often somewhat enlarged, 
and may present a number of dilated veins, which rarely 
amount to a considerable tumor. 
The Breasts enlarge, and may be painful, especialty 
on pressure, and the superficial veins appear as fine, blue 
lines on their surface. The nipple becomes more prom- 
inent, the areola? darker in color, and the glands scat- 
tered about their circle increase in size. SECTION IX. 
Practical Work.1 
1. While the student of embryolog}' can acquire a fair 
knowledge of the subject from text-books, it is desirable 
that some practical work should be done in order that 
he may familiarize himself with the microscopical ap- 
pearances of the various changes which take place during 
the process of development. 
The work itself is fascinating, and the apparatus re- 
quired such as may be found in the armamentarium of 
the general microscopist.2 
For the beginner the study of the embryology of the 
domestic fowl (Gallus domesticus) is best suited, on 
account of the abundance of material always at hand 
and the distinct microscopical pictures presented during 
the various periods of incubation. The lien-embryo has, 
therefore, been taken to illustrate the methods of prac- 
tical work included in this section ; but the directions 
given for hardening, staining, etc., apply equally to all 
embryos. 
2. Apparatus.—A good microscope with one-fourtli 
and two-thirds inch objectives. Higher powers are at 
times useful, but not essential for the beginner. Fine, 
sharp-pointed, straight, and curved scissors,—those used 
by the oculist are the best. Two pairs of fine-pointed 
forceps. A fine scalpel. A section lifter. A razor, 
section knife, or microtome. Several glass individual 
1 The directions given in this section have been taken from articles 
by the author, published in The Transactions of the American Society of 
Microscopists, 1885, and The Microscope, 1888. 
2 Manton, Beginnings with the Microscope. Lea & Shepard, Boston. 96 
HUMAN EMBRYOLOGY. 
salt-cellars. Two or three small glass dishes having 
deep sides. A glass sauce-dish. One or two fruit-jars. 
Glass slides, square cover-glasses, and some fine threads 
of glass, made by drawing out a piece of glass tubing in 
the spirit-lamp or gas flame. 
Reagents.—(a) A 1-per-cent, solution of common salt. 
(b) A 3-per-cent, solution of Chromic acid. 
(c) A solution of Osmic acid. 
Osmic-acid solution (1 per cent.), ... 1 c.c. 
Water, 100 c.c. 
This must be kept in a dark-glass bottle or a bottle 
covered with black paper or plush, as the solution soon 
deteriorates in the light. 
(d) A solution of Picric acid. 
Cold saturated solution of picric acid, . . 100 c.c. 
Sulphuric acid (concentrated), .... 2 c.c. 
Filter and add 
Distilled water, 300 c.c. 
—(Kleinenberg). 
(e) A thin solution of shellac in absolute alcohol. 
(f) Clove-oil collodion. 
Gun-cotton (photographers’), .... 2 grms. 
Sulphuric ether, 15 c.c. 
Alcohol (95 per cent.), 10 c.c. 
Clove-oil, 100 c.c. 
Dissolve the gun-cotton in the ether and alcohol, add 
the clove-oil, and filter (Schallibauin-Gage). 
(g) Alum carmine. 
Aqueous solution of alum (5 per cent.), . . 100 c.c. 
Carmine, 1 grm. 
Boil and, when cool, filter; add a few drops of car- 
bolic acid and cork tight (Grenadier). 
(h.) Haematoxylin. 
Haematoxylin, saturated alcoholic solution, . 4 c.c. 
Ammonia-alum, strong saturated solution, . 150 c.c. PRACTICAL WORK. 
97 
Let stand eight days, filter, and add 
Glycerin, 25 c.c. 
Methyl-alcohol, ....... 25 c.c. 
This stain works best after standing for some weeks 
or months. 
(i) Paraffin. 
Several ounces of paraffin with melting-points at 45° 
and 55° C., or the hardest and softest to be had in the 
shops. These are to be mixed according to the temper- 
ature of the work-room, usually 2 parts of the hard to 
1 of the soft. 
(j) Clove-oil; turpentine-oil ; xylol, or benzoline ; 
spirits chloroform; Canada balsam; concentrated hy- 
drochloric acid; bees-wax, hard and soft. 
The latter is common yellow wax to which enough 
Venetian turpentine has been added to give it the con- 
sistency of putty. 
(k) Celloidin. 
(/) Alcohol, 75 per cent., 95 per cent., and absolute 
( Squibb’s). 
3. Material.—In order to develop the germ in the 
egg, an incubator of some kind is necessary. For this 
purpose a setting-hen may be utilized, or a simple in- 
cubator may be constructed by any tinsmith as follows: 
A strong tin box with copper bottom, having a deep in- 
dentation on one side, is made (Fig. 65). Into the 
indenture two wooden drawers, each with a bottom 
capacity for a dozen eggs, are fitted (c, c) and the whole 
can encased in wood. Between the tin and the wooden 
box there should be room enough to pack a considerable 
amount of cotton or sawdust, to keep the warmth gen- 
erated in the can. The can must be supported on legs 
several inches above the bottom of the wooden box in 
order that a gas-lamp may be placed under it, 98 
HUMAN EMBRYOLOGY. 
The box and can must be perforated above at one 
corner by a tin tube, which is stopped by a large cork 
(&), through which pass the thermometer and the 
thermo-regulator, the latter connected by rubber tubing 
(F, G) on one side with the gas-jet, and on the other 
with the small lamp below (7). 
Probably the best and simplest thermo-regulator is 
that known as “ Reichert’s.” This consists of a tlier- 
Fig. 65. 
mometer-tube filled witli mercury, the upper end of 
which is dilated to receive a glass T-shaped piece, into 
which the gas streams and is conveyed through the 
rubber tube (F) to the lamp below,—the amount of gas 
being regulated by a graduated screw at the back. As 
the temperature increases the mercury in the tube 
rises and stops the aperture in the end of the T-piece, 
thus lowering the gas-flame and maintaining an even 
temperature. The gas is, however, not extinguished, PRACTICAL WORK. 
99 
as a small hole in the side of the T admits just enough 
to keep the flame lighted. A thermometer is placed by 
the side of the regulator, so that the temperature of the 
water with which the can is filled may be determined, 
and the size of the gas-flame regulated accordingly. 
The drawers in the can should be partly filled with 
cotton, in which the eggs are placed and lightly 
covered. 
The water should be kept at 37° to 40° C. Hens’ 
eggs thus incubated hatch in about three weeks. 
Whether the hen or an incubator is employed, the 
eggs used must be newly-laid, in order that the stages 
of development may be accurately studied. Before com- 
mencing incubation the date and hour at which this is 
to begin must be plainty written on the shell with ink, 
and, as the eggs are placed in the incubator, the writing 
should lie uppermost, so that the date may be readily 
seen without disturbing the eggs. 
The first eggs should be removed after about eight- 
een hours' incubation, when the first two layers of the 
blastoderm are well defined. After thirty-six hours the 
three layers, ecto-, meso-, and ento-derm, may be seen. 
The embryos of forty-eight hours, three, four, and 
five days should also be preserved. Older embryos, up 
to the seventh or eighth dajq should be obtained for the 
study of individual organs. 
As soon as one egg is removed from the nest or in- 
cubator, another may be put in its place, and thus in the 
course of a week or ten days a sufficient number of em- 
bryos may be obtained to furnish work for the odd 
hours of many months. 
During incubation the drawers of the incubator 
should be frequently opened and the covering cotton 
removed, in order that the eggs may get plenty of air. 100 
HUMAN EMBRYOLOGY. 
The embryos of reptiles, amphibians, mammals, and 
fish may be obtained as follows :— 
Turtles deposit their eggs in holes, which they dig- 
in the sand along the margin of streams and ponds. 
The time for laying is about sun-down ; the period of 
the year, from the second week in June, varying with the 
locality. The eggs are hatched some time in September 
or October. As soon as a turtle is seen to deposit its 
eggs, these should be carefully removed and planted in 
a box of earth or sand, and covered by wire gauze or 
mosquito-netting. The eggs must be kept moist. As 
incubation is slow, an interval of several days 
should elapse before the first eggs are removed for 
Fig. 66. 
examination. Turtles lay a large number of eggs; so 
that if a nest is found, material will be plenty. 
Frog- and toad- eggs may be found about the 1st of 
June, in streams and ponds. The former occur in 
glairy, gelatinous masses; the latter in glairy, trans- 
parent strings. They should be placed in shallow dishes 
of water, and portions removed and hardened from day 
to day as the embiyo develops. These latter appear 
as dark spots in the centre of the transparent globules. 
The eggs hatch into tadpoles in about six or eight days. 
Fish-eggs and the embryos can best be obtained at a 
hatchery, but, when this is inaccessible, a spawning adult 
fish may be utilized. PRACTICAL WORK. 
101 
“ When a female lisli is in fit spawning condition,” 
says Francis, “the vent becomes slightly enlarged and 
of a reddish tinge. The ova, previously attached to- 
gether by a membrane, become disconnected. Take up 
the fish and hold it, first, head downward, then reverse 
it, and if the great bulk of spawn be seen to shift and 
drop as if from one end of the fish’s belly to the other, 
the eggs are loose and the fish is ready to part with its 
ova.” The method usuall}’ advised for holding the fish 
and expressing the ova is seen in Fig. 60. 
A still better method, introduced by Mr. Glover, is 
to hold the head of the fish with the left hand, seizing 
the tail in the right hand just behind the vent, so as to 
Fig. 67. 
compress the back between the fingers and the palm of 
the hand. The fish is then slightly bent, and the side 
of the thumb rubs against its belly, just above the vent, 
which will cause the extrusion of the eggs. This should 
be done with the fish partly submerged in water. The 
sperm of the male is obtained in the same manner and 
in the same dish, and the eggs and sperm are then gently 
mixed together by means of a feather. The eggs should 
now remain for about two hours undisturbed, and are 
then transferred to the hatching box by means of a 
horn spoon and feather. 
The hatching box, according to Exner, must have 
the floor covered with pebbles, while 1.5 cubic centi- 
metres above this is arranged a layer of glass rods, 102 
HUMAN EMBRYOLOGY. 
about 2 to 4 millimetres from each other, upon which 
the eggs are laid. The box must then be provided with 
running water, the flow being drop by drop, or slightly 
swifter. 
Dead eggs may be recognized by their opacity, 
and should be removed each day. The eggs should be 
examined every twelve hours. 
Mammalian embryos, as of the sheep, etc., be 
obtained at slaughter-houses : for those of smaller ani- 
mals—rabbits, mice,1 etc.—the females must be killed at 
varying periods after fecundation has taken place. The 
abdomen is laid open, the uterus and oviducts dissected 
and spread out, and careful search made with a leus for 
the ova, which must be removed and hardened. 
4. Preparation of the Embryo.—The egg, having 
undergone the required amount of incubation, is care- 
fully removed from the incubator or nest, with the side 
on which the date is written uppermost (for the embryo 
always lies on the top of the yelk), and rested on a 
glass individual salt-cellar. The shell is then broken by 
a sharp rap at the larger end, to let in air. The egg 
and cellar are then transferred to a dish of the salt solu- 
tion, which has been warmed to blood-heat. The depth 
of the salt water should be sufficient to quite cover the 
entire egg. The upper part of the shell must now be 
broken by a few taps of the scissors or scalpel-handle, 
and the pieces removed with fine forceps over the space 
the size of a quarter-dollar, or larger, according to 
the period of incubation. This requires some little care, 
as the sharp-pointed bits of shell are apt to turn inward 
and cut the embryo, or open the yelk. When the shell 
has been removed, the embryo will be seen lying within 
* For this purpose white mice may be utilized, and the exact time of 
copulation noted. PRACTICAL WORK. 
103 
two rings (the area opaca and area pellucida), or in 
the midst of a vascular spot (area vasculosa) varying in 
size according to the time that incubation has progressed. 
A circling cut must now be made around (outside) these 
rings with a pair of fine-pointed, curved scissors, and the 
disc containing the embryo floated off and washed free 
of any adherent yelk by gently agitating it with the 
forceps in the salt solution. 
5. Hardening.—Previous to opening the egg the glass 
sauce-dish should be prepared with a layer of wax, 
about a quarter of an inch deep, at the bottom. This is 
quickly done by pouring melted bees-wax into the dish 
and allowing it to spread out evenly. The dish is then 
partly filled with the Kleinenberg or chromic-acid so- 
lution,1 the embryo transferred to it on a section lifter, 
and the edges of the filmy membrane drawn out and 
pinned down to the wax, so that the embryonic disc 
may harden without wrinkles or distortion. Any kind 
of pins may be used for this purpose, but the long 
German insect pins are the easiest to handle, and are not 
so readily affected by the acid. 
The embryo should be left to harden undisturbed for 
from five to twenty-four hours, according to size. When 
this is accomplished, prepare a glass jar,—a half-pint 
fruit-jar or a tumbler will answer,—with 70-per-cent, 
alcohol, in which a piece of cotton floats just below the 
surface. Upon this cotton lay the embryo, and allow it 
to remain until the alfcohol has withdrawn the picric 
acid and the specimen has become whitened. It is fre- 
quently necessary to change the alcohol several times 
before this is accomplished. When the embryo is quite 
bleached it may be placed in 95-per-cent, alcohol for 
indefinite keeping. 
* This renders the embryo more brittle than the picric-acid solution, 104 
HUMAN EMBRYOLOGY. 
When the chromic-acid solution is employed for hard- 
ening, the subsequent method of procedure is the same 
as that just given, except that the hardened specimen 
is transferred to a jar of water instead of alcohol. When 
washed free from the acid, which requires some little 
time, the embryo is first placed in 70-per-eent. alcohol 
and then stained, or in 95-per-cent, alcohol for keeping. 
6. Staining.—Embryos may be stained in toto or 
after the sections have been placed on the slide. The 
former method will be found the simplest and most con- 
venient for general practice. 
If it is desired to stain the embryo at once after 
hardening and placing in 70-per-cent, alcohol, it must 
first be washed in water (if it is a picric-acid specimen, 
but not if chromic acid has been used), and then placed 
ill the stain, where it should remain for several hours, 
according to the size of the embryo. Practice alone 
will teach the avoidance of either over- or under- stain- 
ing. The specimen is then washed again in 70-per-cent, 
alcohol made slightly sour by the addition of a drop or 
two of concentrated hydrochloric acid. Thus stained, 
the embryo may be preserved in 95-per-cent, alcohol 
ready for imbedding at some future time. 
Staining on the Slide.—After the imbedding material 
has been removed by the proper solvents, which may 
require from 15 to 20 minutes (see 13 and 14, pages 109 
and 110), the slide is rinsed in 95-per-cent, alcohol and 
placed immediately in the stain'if this is an alcoholic 
solution, but if an aqueous solution it is first washed in 
water. On removing from the stain, wash in alcohol or 
water, as the case may be; if the latter, a second washing 
in alcohol must be given the slide. The sections are 
then cleared and mounted as given under 13, page 109. 
7. Infiltrating.—Before sections of the delicate embryo PRACTICAL WORK. 
105 
can be made it must first be infiltrated and imbedded in 
some material which will hold it firmly without injuring 
its tissues. For this purpose paraffin and eelloidin are 
best suited. 
8. Paraffin Method.—The specimen is first placed in 
absolute alcohol for several hours until it is thorougly 
dehydrated, and then in a vial of chloroform, where it 
may soak for some time longer. It is then transferred 
to a watch-glass containing chloroform and fine shavings 
of hard and soft paraffin (1 to 5). The watch-glass must 
now be carefully heated, either in what chemists call a 
double drying-jacket (which is similar to the tin can 
Fig. 68. 
of the incubator already described, wire shelves replac- 
ing the drawers), kept at about 113° F.,or over a water- 
batli, until the paraffin is melted and the chloroform 
evaporated. This properly takes from twelve to twenty- 
four hours, and is done in order that all traces of alcohol 
and chloroform may be driven off and the embryo become 
thoroughly permeated with the paraffin. The embryo 
is then arranged at one end of a paper cell, which has 
previously been partly fdled with melted paraffin and 
the latter allowed to cool, and covered with warm 
paraffin. 
9. The Paper Cell and Imbedding.—The cell may he 106 
HUMAN EMBRYOLOGY. 
made of stiff glazed paper, cardboard, or like material. 
A convenient shape for small embryos is one and a half 
inches long by three-fourths wide and half an inch 
deep. Having cut the paper the required size, begin by 
folding down each side of a width to give the cell the 
necessary depth, and over them the ends a little wider 
than the sides. On opening the paper a small square 
will be seen at each corner marked out by the folds 
(a, 6, A, Fig. 68). Now bring the end fold of one of 
these squares exactly against the side fold of the same 
square, and draw the intermediate paper (A, b) between 
the thumb and finger, which divides each square into 
two triangles. Turn the triangle over the end of the 
cell and repeat on the other side. A complete end is 
thus formed to the cell. To hold the triangles in place 
and keep the end from unfolding, turn the top of the 
end paper—which projects a little above the level of 
the sides—over them (A, 2, a). Prepare the other end 
of the cell in the same way. It is important that the 
folds at the corners meet exactly, or the cell will be 
irregular in shape. 
This cell is then about half-filled with melted paraffin, 
which is allowed to cool, and the embryo placed in it in 
the direction in which it is desired to make the sections. 
When the embryo has been arranged in the cell, a 
little warm paraffin should be poured over it and left 
until it sets a little to fix the specimen, and then the 
cell must be filled with the liquid paraffin. 
Should the embryo float out of place during the im- 
bedding process it may be returned to any position de- 
sired, while the paraffin is still fluid, by the point of a 
hot needle. Air-bubbles, which frequently collect about 
the object, should be displaced b}r the hot needle before 
the upper layer of the paraffin has become hardened. 107 
PRACTICAL WORK. 
Specimens imbedded in this way may be kept almost 
indefinitely if not subjected to heat. 
If it is desired to cut ribbon sections, the paraffin 
used should be that having the lowest melting-point. 
When cold it must be carefully cut away around the 
embryo, a sixteenth of an inch being left on each side, 
and the embryo re-imbedded in paraffin having a higher 
melting-point. The reason for this will be explained 
under “ Section-Cutting,” page 109. 
10. Celloidin Method.—After hardening, and staining 
if desired, embryos may be placed for a few days in a 
thin solution of celloidin, and then transferred to a 
thicker solution, where they may be left for a week or 
even longer without injury. A cork is then wrapped 
with stiff paper, the latter projecting an inch or more 
beyond the former, and the top of the cork moistened 
with celloidin. When this has partially hardened it is 
slightly wet with ether, the embryo placed upon it in 
the desired position, and the cell then filled up with the 
celloidin. After exposing this to the air until a film has 
formed on top, the cork is carefully lowered into a jar 
of 75-per-cent, alcohol and left to harden. In order to 
keep the cork in the upright position it will be neces- 
sary to impale it on a weighted pin,—that is, a pin 
fastened to a little solder, which must be of sufficient 
weight to hold the cork in place. 
After a few days the paper may be removed, and the 
embryo will be found firmly imbedded in the transparent 
celloidin. 
11. Preparation of the Slide.—As the sections must 
be serial and laid upon the slide in regular order so that 
the parts may be studied with exactness, it is necessary 
that a number of glass slides be in readiness. The latter 
must be perfectly clean and clear. Each slide in turn 108 
HUMAN EMBRYOLOGY. 
should be warmed over the spirit-lamp flame; and when 
the moisture that collects on the application of the heat 
disappears, a glass rod dipped in the shellac solution is 
pushed over the slide in such a way as to leave behind 
it a thin film of the lac. This may easiest be accom- 
plished by running the rod across the glass, and then 
quickly drawing it over the length of the slide. It is 
not necessary, however, that over an inch of surface 
should be covered by the shellac. If the film left should 
turn opaque, it indicates that the glass was not hot 
enough, and in that condition the slide is unfit for use. 
The film should be perfectly smooth, free from waves, 
and so thin as to be perceptible onty by the iridescent 
hue which it imparts to the glass. 
When ready to make sections, a slide should be 
selected and a thin coating of clove-oil given it, with a 
fine camel-hair brush, over that portion covered by the 
film. Care must be taken not to go over the same spot 
twice, as the oil dissolves the varnish. Instead of the 
method just described, the slide may be painted with a 
thin layer of the Schallibaum clove-oil collodion just 
before using. 
12. Section-Cutting.—Sections are made in three 
directions : (1) at right angles to the long axis of the 
body,—transections ; (2) parallel with the long axis of 
the body, and passing from left to right,—dextro-sinis- 
ti'al longisections ; (3) parallel to the long axis of the 
body, and passing from dorsal to ventral aspects of the 
body,—dorso-ventral longisections. 
For sectioning embryos a microtome is almost indis- 
pensable, but fair sections may be made with the razor 
or knife by one used to free-hand cutting. The labor 
is much greater, however, and the sections vary greatly 
in thickness. Before sectioning, the paraffin cast in 109 
PRACTICAL WORK. 
which the embryo is imbedded should be trimmed 
down to within a few lines of the object (Fig. 68, B), 
straight behind and triangular in front (Fig. 69, A). 
Each consecutive section, as removed, must be laid on 
the prepared slide, beginning at the upper right-hand 
corner and continuing in rows from right to left. Care 
must be taken that a little less space is occupied than 
the size of the cover-glass to be used. 
If the microtome is used the sections have a tendency 
to roll up as they are cut, but this may be prevented 
by holding the point of a teasing-needle or a camel-hair 
brush just over the edge of the knife as it passes through 
Fig. 69, 
the paraffin ; or, one of the numerous planishers, to be 
had of dealers in microscopical supplies, may be used. 
In making ribbon sections the embryo must be im- 
bedded as directed on page 107 (section 9). If the par- 
affin surrounding the embryo is of the proper consist- 
ency, each section as cut will adhere to the edge of the 
one in front of it, and a strip of any desired length may 
be had (B, Fig. 69). For ribbon sections a microtome 
is indispensable. 
13. Mounting—Paraffin Method.—When a sufficient 
number of sections have been placed, the slide should be 
carefully warmed over the spirit-lamp flame, taking care 110 
HUMAN EMBRYOLOGY. 
not to heat it too hot. This melts the paraffin, dispels 
the clove-oil, and permanently fixes the section. By 
allowing the slide to rest on its edge for a few minutes 
the paraffin will run down and collect at one point. 
When the slide is cool a few drops of oil of turpentine 
should be poured over the sections to dissolve the re- 
maining paraffin and clear the sections. The length of 
time during which the turpentine should cover the ob- 
ject depends upon the size of the latter and the amount 
of paraffin left in the tissues. The oil must then be run 
off and the slide carefully wiped clean up to the sec- 
tions. A drop of Canada balsam 1 and the adjusting of 
the cover-glass complete the procedure. 
14. With the Schallibaum clove-oil collodion, after 
heating, the slide is left to cool, and then immersed in 
a solvent, such as benzin, xylol, chloroform, turpentine, 
etc., to get rid of the imbedding material. It is then 
rinsed in 95-per-cent, alcohol and cleared in the follow- 
ing agent:— 
Turpentine, 3 parts. 
Carbolic acid, 2 parts. 
The sections are then protected by a cover-glass 
which has received a thin coating of the following:— 
Pure Canada balsam, 25grms. 
Chloroform, 2 c.c. 
Clove-oil, 2 c.c. 
The clove-oil dispels all cloudiness (Gage).2 
15. Celloidin sections may be treated thus: After 
fixing on the slide as in section 14, pour over the sec- 
tions 95-per-cent, alcohol, and then dissolve out the 
celloidin with a few drops of ether and absolute alcohol. 
1 Dr. Minot recommends the use of very thin balsam,—pure balsam 
diluted with a large quantity of pure benzol.—The Microscope, May, 1888, 
p. 137. 
3 Proceedings of the American Society of Microscopists, 1884, p. 202. PRACTICAL WORK. 
Let these nearly evaporate, wash again in 95-per-cent, 
alcohol, clear, and mount as in section 14. 
16. Embryos as Transparent Objects.—From the salt 
solution the embryo is pinned out in a little of the 
osmic-acid solution, in which it is kept until it acquires 
a light-brown color. It is then washed for some time in 
water to remove the acid; after which it is placed in 70- 
per-cent. alcohol, then in absolute alcohol, which latter 
must be changed once, and finally in clove-oil to clear 
up. This completed, the embryo is ready for mounting. 
Having a clean slide ready, place a drop of Canada 
balsam on its centre and lay the embryo on this. All 
the clove-oil is then run off, by gently tipping the slide, 
wiped away, and another drop of balsam allowed to fall 
upon the object. The corners of the cover-glass are 
now tipped with wax to slightly raise them from the 
specimen, and the cover adjusted. 
On either side a hair of spun glass must be run 
beneath the cover-glass to keep this permanently from 
resting upon the embryo. When the balsam becomes 
dry, the wax on the cover-glass may be removed. Em- 
bryos may be treated in this manner up to the forty- 
eighth hour, but after that they are rather too large for 
transparent objects. 
IT. Labeling.—A label having the name of the 
preparer neatly printed on it should be gummed to 
eaeli end of the finished slide. On one label the place 
of mounting and the date are filled in with ink. At the 
upper left-hand corner the series to which the slide 
belongs is noted in Roman numerals, while just below 
it, in Arabic numerals, is written the number of the 
slide in the series, thus :— 
Series X. 
No. 5. 112 
HUMAN EMBRYOLOGY. 
On the label at the other end of the slide is written 
the kind of section (transection, longisection, etc.), the 
variety and age of the embtyo, and the hardening, stain- 
ing, and mounting agents which have been employed. 
18. Slide-Cabinet.—Any kind of a cabinet may be 
used in wdiich to preserve the slides from injury and 
dust. A very convenient receptacle is a strong paste- 
board box, with hinged front, holding ten or more paste- 
board trays. Each tray should be divided into two or 
three compartments, which will hold from six to nine 
slides each, on the flat. A. GLOSSARY 
OF SOME OF THE 
Words and Terms used in Embryology. 
Allantois (Gr. dXXas, a sausage ; eldos, like)—A tubular diver- 
ticulum from the archenteron, extending to the chorion 
and conveying blood-vessels. Concerned in the formation 
of the bladder and urachus. 
Amnion (Gr. dpvls, a young lamb ; first observed in embryo 
of this animal)—A double membrane, the innermost layer 
of which envelops the embryo. 
Anal plate—A bridge of tissue which temporarily closes the 
anal canal. 
Anlage (Ger.)—Rudiment. 
Archenteron (Gr. apxij, beginning; ivrepov, intestine) — The 
primitive gastro-intestinal canal. 
Archiamphiaster (Gr. apxbeginning; apipl, on both sides; 
auT-fip, a star)—The star-like arrangement of the proto- 
plasm at the ends of the nuclear spindle. 
Blastocele (Gr. pXaaris, germ ; Kofawpa, hollow)—The segmen- 
tation cavity. 
Blastoderm (Gr. /SXao-nk, germ ; Uppa, skin)—The external 
layer of the segmented ovum. Later the blastoderm con- 
sists of three layers. 
Blastodermic vesicle—The vesicle formed by the collection 
of fluid within the blastula. 
Blastophore (Gr. pXao-ris, germ ; Tripos, pore)—A small opening 
at the anterior end of the primitive streak, leading at first 
into the notochordal canal, and later into the archenteron. 
Blastula—The stage following completed segmentation, in 
which the ovum is a hollow sphere filled with fluid and 
bounded by the blastoderm. 
Brain (Fore, Mid, Hind)—The anterior, middle, and posterior 
divisions of the neural canal. The cerebral vesicles. 114 
GLOSSARY. 
Branchial clefts (Gr. ppdyxLa> gills of fishes)—Visceral 
clefts. 
Caduca (Lat. cadere, to fall)—Decidua. 
Cerebral vesicles—Brain. 
Chorion (Gr. x^Pl0V> foetal membranes)—Primitive, the shaggy, 
villous covering of the unattached ovum developed from 
the blastoderm. G. Iceve, the outermost envelope of the 
ovum in contact with the decidua reflexa. The G. fron- 
dosum is in contact with the decidua serotina. 
Chromatin—The fine reticulated net-work of the cell-nucleus, 
so called from its strong affinity for staining fluids. Achro- 
matin does not readily take colors. 
Cicatricula (Lat. diminutive of cicatrix)—Germinal disc. A 
small white disc situated at the animal pole of the hen’s 
egg. 
Cloaca (Lat. cloaca, sewer)—The terminal (caudal) portion of 
the intestine. 
Coelom (Gr. solXup.a, cavity)—The body-cavity, or space be- 
tween the somatopleural and splanchnopleural walls. 
Conus medullaris—The lower end of the spinal cord between 
the lumbar enlargement and the filum terminale. 
Corpus albicans (Lat. alius, white)—The decolorized clot 
found in a degenerating corpus luteum of pregnancy. 
Corpus hsemorrhagicus—The clot which forms in the empty 
Graafian follicle immediately after its rupture. 
Corpus luteum (Lat. corpus, body; luteus, yellowr) — The 
yellow body formed in the Graafian follicle following 
rupture. G. 1. verum, or true, forms in pregnancy. G. 1. 
spurium, or false, in menstruation. 
Cotyledon (Gr. kotvX7]8J>v, socket or cup)—The small, squarish 
lobes of the maternal surface of the placenta. 
Covering layer—The primitive external layer of the blasto- 
derm. 
Daughter=cells—The cells resulting from the division of the 
mother-cells in spermatogenesis. 
Decidua—The thickened, spongy lining of the uterine cavity 
in pregnancy. D. vera, all the lining of the cavity except 
the D. reflexa, that portion which is reflected over and in- 
closes the ovum, and D. serotina, that portion upon which 
the ovum rests. GLOSSARY. 
115 
Deutoplasm (Gr. Sevrepos, second ; -ir\d.irp.a, formed matter)— 
The food-yelk. 
Discus proiigerus—A mass of cells surrounding the ovum 
within the Graafian follicle. 
Ectoderm (Gr. &t6s, external; 5£pp.a, skin)—The external layer 
of cells of the blastoderm. 
Embryo (Gr. efifipvov, the young in the womb)—The products 
of conception up to the fourth month of gestation. 
Embryonic area—The area within which the embryo is de- 
veloped. 
Entoderm (Gr. tvdov, within ; Sippxt, skin)—The innermost 
layer of cells of the blastoderm. 
Epitrichium (Gr. iirl, upon ; Opl£, hair)—The delicate, most 
external layer of cells of the epidermis found in young 
embryos. 
Foetus (Lat. foetus, offspring)—The young animal from the 
fourth month to the end of gestation. 
Filum terminate—The thin, drawn-out portion of the lower 
end of the spinal cord. 
Folds {Head, Tail, Side)—Grooves by which the embryo is con- 
stricted off from the remainder of the blastodermic vesicle. 
Foregut—The cavity shut off just below the notochord by 
the deepening of the head-fold. 
Gaertner’s duct—The persisting lower portion of the Wolffian 
duct. 
Gastrula (Gr. yaur-np, belly)—An embryonic stage supposed 
to be common to all animals. Gastrulation consists in a 
process of invagination of the blastula. 
Genital cord—The posterior united portions of the urogenital 
ridges. 
Genital eminence—A thickening of the anterior portion of 
the anal plate ; the anlage of the penis and the clitoris. 
Genital ridge—A paired ridge developed from the posterior 
wall of the coelom median to the Wolffian body, and from 
which arise the sexual glands. 
Genoblast (Gr. ytvos, race ; jSXcurn5s, germ)—A sexual element, 
either male or female. 
Germinal area—See “Embryonic area.” 
Germinal spot—Nucleolus of the ovum. 
Germinal vesicle—Nucleus of the ovum. 116 
GLOSSARY. 
Germinating cells—Cells developed from the epithelium of 
the medullary tube, which give rise to the neuroblasts. 
Gill=clefts—Visceral clefts. 
Graafian follicle—The ovarian vesicle containing the ovum. 
First described by Reinier de Graaf in 1672. 
Impregnation—The fertilization of the female element by 
that of the male. 
Karyokinesis (Gr. K&pvov, a nut ; kAtjo-is, motion)—Indirect 
cell-division. 
Knot, Hensen’s—The point at which the two blastodermic 
layers are first included in the primitive streak. 
Lanugo (Lat. lana, wool)—The downy hairs which cover the 
foetus from the fifth month of utero-gestation. 
Lateral plates—A longitudinal thickening of the dorsal meso- 
derm on either side of the notochord. 
Lenticular body—The mass of cells crowded to one point in 
the blastula. 
Liquor amnii—The fluid in which the embryo floats in the 
amniotic sac. 
Lutein (Lat. luteus, yellow)—A peculiar, crystallizable sub- 
stance which gives rise to the yellow color of the corpus 
luteum and coagulated blood. 
Maturation—The ripening of the ovum preparatory to im- 
pregnation. 
Medullary folds — The upgrowing sides of the medullary 
plates. 
Medullary groove—A groove formed by the upgrowth of the 
medullary folds. 
Medullary plates—A thickened portion of the ectoderm on 
either side of the median axillary line of the embryo. 
Menstruation (Lat. memtruus, monthly)—The phenomena 
associated with the periodical discharge of blood from the 
female genitals. 
Mesencephalon (Gr. pA<xos, middle; iyictyaKov, brain)—The 
midbrain. 
Mesenchyma (Gr. pAtros, middle ; iyxvpa, infusion)—Em- 
bryonic connective tissue. 
Mesoblastic somites—Proto vertebrae. 
Mesocolon (Gr. k6\ov, colon)—The embryonic mesentery con- 
nected with the large intestine. GLOSSARY. 
Mesoderm—The second cell-layer of the blastoderm ; derived 
from both (?) the ecto- and ento- dermal layers. 
Mesogastrium (Gr. yaari/p, stomach)—The greater omentum. 
Mesonephros (Gr. ve<pp6s, kidney)—The Wolffian body. 
Mesorchium (Gr. 8pias, testicle)—The suspensory ligament of 
thej;esticle. 
Mesorectum—A fold of peritoneum between the upper part 
of the rectum and the sacrum. 
Mesothelium (Gr. #17X77, nipple)—The epithelium lining the 
eoelomic cavities (Minot). 
Mesovarium (Lat. ovarium, ovary)—The suspensory ligament 
of the ovary. 
Micropyle (Gr. pu<p6s, small ; 71-11X77, entrance)—A passage in 
the envelopes of the ovum through which the spermato- 
zoon penetrates. 
Morula (Lat. morus, mulberry)—-The mulberry-like mass of 
spheres resulting from segmentation of the yelk. 
Mother=cells—The three cells resulting from the division of 
the parent-cell. 
Muller’s duct—A paired tubular duct developed from the 
Wolffian body and running parallel with the Wolffian 
duct. The anlage of the Fallopian tubes, uterus, and 
vagina in the female. 
Myotomes (Gr. pus, muscle ; ripveiv, to cut)—The proximal por- 
tion of the protovertebrse from which develop most of the 
voluntary muscles of the trunk and the vertebral column. 
Nephridia (Gr. ve<J>p6s, kidney; <L8os, shape)—See “Segmental 
tubules.” 
Nephrotome (Gr. ve<f>p6s, kidney ; rop.ii, section)—The inter- 
mediate cell-mass ; the distal portion of the protovertebne, 
in which are developed the segmental tubules and ne- 
phridia. 
Neuroblasts (Gr. vevpov, nerve ; /3Xa<rr6s, germ)—Young nerve- 
cells. 
Notochord (Gr. vCnov, the back ; x°P^7> chord)—A longitudinal 
rod of cells separated off from the entoderm, just below 
the medullary groove. The anlage of the spinal column. 
Oosperm—The ovum after the fusion of the two pronuclei. 
Oral plate—A point between the forebrain and the heart, 
where the mesoderm is absent and ecto- and ento- derm 
unite ; rupture of which gives rise to the mouth. 118 
GLOSSARY, 
Ovulation—The rupture of the Graafian follicle and escape of 
the ovum. 
Ovum—The female generative cell or egg. 
Parent=cell—A large cell lying near the tunica propria of the 
testis, which divides into the mother-cells in the process 
of spermatogenesis. » 
Parthenogenesis (Gr. vopSivos, virgin ; ybveais, to beget)—Self- 
fertilization. 
Perivitelline space (Lat. peri, around ; mtellus, egg)—The 
space between the vitelline membrane and zona pellucida. 
Plastids—Non-nucleated adult red blood-corpuscles (Minot). 
Pfliiger’s cords—Cord-like epithelial ingrowths of the ovary 
which include the primitive ova. 
Polar globules—The rounded masses of nuclear material ex- 
truded between the yelk and zona pellucida during matu- 
ration of the ovum. 
Primitive streak—A median axial thickening of the cells of 
the ectoderm extending from near the centre of the em- 
bryonic area caudalward. 
Proamnion—A part of the germinal area in front of the head 
in which for a time the mesoderm is absent. 
Proctodmum (Gr. wpotcrbs, anus ; oSaios, on the way)—A pit- 
like depression at the caudal end of the embryo which 
gives rise to the cloacal opening. 
Pronephros (Gr. irpi, before ; ve<f>pbs, kidney)—The anterior 
portion of the Wolffian ridge, situated immediately behind 
the heart. The head-kidney. 
Pronucleus—Female: The nucleus remaining in the ovum 
after extrusion of the polar globules. Male: The head of 
the spermatozoon after its entrance into the ovum. 
Prosencephalon—The forebrain. 
Protovertebral somites—Squarish-shaped bodies formed by 
the cleavage of the lateral plates. 
Purkinje’s vesicle—The nucleus of the ovum. 
Segmental duct—See “Wolffian duct.” 
Segmental tubules—The tubules of the pronephros. 
Segmentation—The division of the impregnated ovum into 
numerous spheres. Holoblastic, when the entire ovum 
participates in the segmentation (mammals) ; Meroblastic, 
when the division is limited to a part (birds) ; Discoidal, 
when a circular patch (hen’s egg). GLOSSARY. 
119 
Segmentation cavity—The cavity of the blastula stage ; the 
space within the segmented ovum. 
Sertoli’s ceils—Large cells found in the second layer of the 
seminiferous tubules. 
Smegma—See “ Vernix caseosa.” 
Somatopleure—Body-wall. 
Sperm-cell—See “ Spermatozoon.” 
Spermatoblasts—The transformed daughter-cells from which 
the spermatozoa are developed. 
Spermatocysts—Daughter-cells. 
Spermatogenesis (Gr. cnrtpua, seed ; ytweu, to beget)—The 
formation of the spermatic cells. 
Spermatozoon (Gr. Dor, animal)—The essential male element 
in the process of fertilization. 
Spindle-shaped body—Fine thread-like bands appearing in 
the nuclear substance preparatory to the extrusion of the 
polar globules. 
Splanchnopleure—Walls of the digestive tract. 
Spongioblasts—Young neuroglia-cells. 
Stigma (Gr. arLypa, point)—Point of rupture of the Graafian 
follicle. 
Stomodaeum (Gr. <tt6imi, mouth ; ScUu, to divide)—A pit-like 
depression at the cephalic end of the embryo from which 
the orifice of the mouth is developed. 
Thalmencephalon—The ’tween brain. 
Umbilical vesicle—The yelk-sac after the folding off of the 
embryo. 
Urachus (Gr. otipov, urine ; to hold)—The remains of the 
allantois extending from the bladder to the umbilicus. 
Urogenital ridges—The ridges formed by the uniting of the 
Wolffian and genital ridges. 
Vernix caseosa—A whitish, greasy substance formed of the 
secretions of the sebaceous glands mixed with epithelium, 
and found on the surface of the foetus after the fifth 
month. 
Visceral arches—The tissue between the visceral clefts, con- 
cerned in the development of the lower jaw, bones of ear, 
hyoid and thyrohyoid bones. 
Visceral clefts—Pouches arising in the entoderm of the phar- 
ynx, and concerned in the development of the ear, tonsils, 
thymus and thyrohyoid glands. 120 
GLOSSARY. 
Vitelline membrane—The covering developed from and lying 
in contact with the yelk. 
Vitellus—The yelk. 
Wagner’s spot—The nucleolus of the ovum. 
Wolffian body—A series of tubules developed from the Wolf- 
fian ridge and opening into the duct. The anlage of the 
kidney. 
Wolffian duct (Segmental duct) — A paired, longitudinal, 
tubular duct, formed probably from the ectoderm and 
running caudalward between the proto vertebrae and the 
point of junction of the somatopleure and splanclino- 
pleure, and opening into the cloaca. The first indication 
of the genito-urinary apparatus. The upper portion per- 
sists in the female as the parovarium ; iii the male as the 
epididymis. 
Wolffian ridge—A paired ridge on the dorsal surface of the 
body-cavity, containing the Wolffian and Mullerian ducts. 
Zona pellucida—The external envelope of the ovum. 
Zona radiata—See “Zona pellucida.” INDEX. 
Alae nasi, 81 
Alimentary tract, 65 
Allantois, 49 
Amnion, 47 
development of in hen em 
bryos, 47 
in human embryos, 48 
Amniotic fluid, 48 
cavity, 48 
Anterior chamber, eye, 84 
nares, 81 
vitelline veins, 55 
Antihelix, 84 
Antitragus, 83 
Anus, primitive, 72 
Aorta, dorsal, 57 
Aortic arches, 56 
Aqueduct of Sylvius, 61 
Archenteron, 68 
Area, embryonic, 40 
germinal, 10 
Arm, 80 
Arteries, aortae, primitive, 56 
carotids, 56 
ductus Botalli, 57 
iliac, 57 
omphalo mesenteric, 56 
pulmonary, 57 
subclavian, 56 
vertebral, 56 
Auditory canal, 68-82 
ganglion, 82 
vesicle, 82 
Bauchstiel, 49 
Bile-duct, 70 
Bladder, 24-64 
Blastodermic membrane, 37 
vesicle, 37 
Blastula, 37 
Blood, corpuscles, primitive, 57 
maternal, in pregnancy, 92 
vessels, 55 
Brain, 59 
gray matter of, 59 
white matter of, 59 
Branchial arches, 68 
clefts, 68 
Breasts, child’s, at birth, 88 
maternal, in pregnancy, 88 
Breathing, child’s, at birth, 88 
Broad ligaments, 78 
Budding, 2 
Caecum, 70 
Caput succedaneum, 86 
Cardinal veins, 57 
Carotid arteries, external, 56 
internal, 56 
Cauda equina, 59 
Cell, daughter, 27 
mother, 27 
parent, 27 
Ceplialhaematoma, 86 
Cerebellum, 62 
Cerebral flexures, 60 
hemispheres, 61 
lobes, 61 
vesicles, primary, 59 
Cervix uteri in pregnancy, 94 
Child at birth, 86 
Chorion, 46 
frondosum, 47 
laeve, 47 
Chorionic vesicle, 46 
Choroid, 84 
Choroidal fissure, 84 
Circulation, child’s, at birth, 87 
placental, 51 
primary embryonic, 55 
Clitoris, 72-75 
Cloaca, 72 
Cloacal opening, 72 
Cochlea, 82 
Coelom, 40 
Colon, 70 122 
INDEX. 
Commissures, 11 
Conjugation, 3 
Conus medullaris, 58 
Cornea, 83-84 
Corpora quadrigemina, 61 
Corpus callosum, 61 
hsemorrhagicum, 31 
luteum, menstrual, 31 
in pregnancy, 32 
uteri, 15 
Covering layer, 37 
Decidua, 45 
reflexa, 46 
serotina, 44 
vera, 46 
Development, sexual, 3 
Duct, Gaertner’s, 78 
omphalo-mesenteric, 44 
vitelline, 44 
Wolffian, 63 
Ductus Botalli, 57 
Duodenum, 70 
Ear, external, 82 
internal, 81 
Ectoderm, 38 
Embryo, 1 
and foetus at different months 
of development, 89 
folding off of, 42 
Embryology, definition of, 1 
Embryonic area, 40 
Entoderm, 38 
Epididymis, 77 
Epiglottis, 68 
Epi-oophoron, 22 
Eustachian tube, 82 
Excretions, child’s, at birth, 89 
External genitals, 72 
during pregnancy, 94 
Extremities, development of, 79 
Eye, 83 
Eyelids, 85 
Eyes at birth, 88 
Face, 80 
Fallopian tubes, 17, 76, 77 
Female organs of generation, 6 
Filum, externum and internitm, 
58 
Fingers, 80 
Fission, 2 
Foetus, 1 
Fold, head, 44 
tail, 44 
Folding off of embryo, 42 
Follicles, Graafian, 22-31 
Foramen of Monro, 61 
Forearm, 80 
Forebrain, 60, 61 
permanent, 61 
Foregut, 44 
Fornix cerebri, 61 
Fourcliette, 11 
Function, male, 4 
Fundus uteri, 16 
Fusion, 3 
Gall-bladder, 70 
Gemmation, 2 
Genital cord, 17 
eminence, 72 
fold, 76 
groove, 72 
labia, 72 
ridge, 75 
Genoblast, 4 
Germinal area, 40 
epithelium, 76 
spot, 29 
vesicle, 29 
Gill-clefts, 68 
Gland, Bartholin’s, 9 
Cowper’s, 9 
Duvernay’s, 9 
reproductive, male, 4 
Tiedeman’s, 9 
vulvo-vaginal, 9 
Gians penis, 74 
Glottis, 72 
Graafian follicles, 22-31 
Gums, 81 
Head, child’s, at birth, 86 
measurement of child’s, 87 
Head-bend, primary, 60 
Head-fold, 44 
Heart, development of, 53 INDEX 
123 
Helix, 83 
Hensen, knot of, 40 
Hindbrain, 60, 62 
Hindgut, 44 
Hydatids of Morgagni, 77 
Hymen, 12 
Hyoid bone, 68 
Iliac arteries, 57 
Impregnation, 33 
Incus, 68 
Inferior maxillary, 67 
Intestine, 69 
Iris, 84 
Kidneys, 62 
Labia, majora, 7, 75 
minora, 8-75 
Lanugo, 48 
Larynx, 72 
Leg, 80 
Lens, eye, 83 
Lenticular body, 37 
Leucocytes, 57 
Lip, 81 
Liquor amnii, 48 
folliculi, 22 
Liver, 70 
maternal, in pregnancy, 93 
Lungs, 71 
capacity of, maternal, in preg 
nancy, 93 
Male, function of, 4 
Malleus, 68 
Mandibular process, 67 
Maternal organism, changes in, 
in pregnancy, 91 
Maturation of ovum, 29 
Maxillary process, 67 
Maxilla, inferior, 67 
superior, 67 
Meconium, 89 
Medulla oblongata, 62 
Medullary canal, 41 
folds, 41 
groove, 41 
plate, 41 
Membrane, vitelline, 28 
Menstruation, 35 
Mesentery, 69 
Mesoderm, 38 
Metazoa, 1 
Midbrain, 60, 61 
Midgut, 66 
Mous veneris, 7 
Morula, 36 
Mouth, 66 
Muller’s duct, 75 
Muscle-plate, 79 
Muscular system, 79 
Myotome, 79 
Nails, 80 
child’s, at birth, 88 
Nasal bridge, 81 
groove, 81 
passages, 81 
pits, 80 
process, 81 
Neck-bend, 61 
Neplirotome, 79 
Nervous system, central, 57 
Neural canal, 41 
Nose, 80 
Notochord, 41 
Nucleus, first segmentation, 35 
Nymphae, 8 
(Esophagus, 68 
Olfactory lobes, 62 
plates, 80 
Omentum, 69 
Omphalo-mesenteric arteries, 56 
duct, 44 
vein, 56 
Ontogeny, 1 
Oosperm, 35 
Optic nerve, 61, 84 
vesicles, 61 
Oral plate, 66 
Organ of Rosenmuller, 22 
Organism, plianges in, at pu- 
berty, 3 
Organs of generation, female, 
external, 6 
internal, 12 
Ossification, 78 
Osteophytes, 92 
Nails, 80 
Nose, 80 124 
INDEX. 
Otocyst, 82 
Ova, 77 
Ovaries, 19 
Ovary, 77 
Ovulation, 31 
Ovum, 27 
maturation of, 29 
migration of, 32 
Pancreas, 70 
Parovarium, 22, 78 
Parthenogenesis, 30 
Penis, 72, 74 
Perineum, 9, 74 
Pfliiger, cords of, 77 
Pharynx, 67 
Phylogeny, 1 
Placenta, 50 
Pleural sacs, 72 
Polar globules, 30 
Pons Yarolii, 62 
Posterior vitelline veins, 56 
Practical work, 95-112 
Primary embryonic circulation, 
55 
layers, 37 
optic cup, 83 
Primitive aortse, 56 
streak, 40 
Proamnion, 39 
Processus globularis, 81 
Pi’onucleus, female, 30 
male, 34 
Propagation of species. 2 
Prostate gland, 74 
Prostatic vesicle, 75 
Proto vertebrae, 42 
Protozoa, 1 
Puberty, 3 
Pulmonary artery, 57 
Pupil, 84 
Purkinje, vesicle of, 29 
Recessus vestibuli, 82 
Rectum, 23 
Rete testis, 77 
Retina, 83 
Rosenmiiller, organ of, 22 
Schneiderian membrane, 81 
Sclera, 84 
Scrotum, 75 
Secondary optic cup, 83 
embryonic circulation, 56 
Segmental duct, 63 
Segmentation, 36 
cavity, 37 
lioloblastic, 37 
meroblastic, 36 
nucleus, 35 
Semen, 5 
chemistry of, 5 
Semicircular canals, 82 
Seminal canals, 77 
fluid, 5 
Sexual cord, 77 
development, 3 
gland, 76 
Sinus terminalis, 55 
Skeleton, 78 
Skin, child’s, at birth, 88 
maternal, in pregnaney, 93 
Somatopleure, 40 
Somites, 42 
Species, propagation of, 2 
Sperm-cells, 77 
Spermatogenesis, 26 
Spermatozoon, 25 
Spinal cord, 57 
cervical enlargement of, 59 
columns of, 58 
lumbar enlargement of, 59 
nerves, 57 
Splanclmopleure, 40 
Spleen, 71 
Spore formation, 3 
Spot of Wagner, 29 
Stigma, 22 
Stomach, 69 
Subclavian artery, 56 
Superior maxilla, 67 
Suprarenal capsules, 64 
Tail-fold, 44 
Testicles, 4, 77, 88 
Thigh, 80 
Thymus gland, 68 
Thyrohyoid bone, 68 
Thyroid gland, 68 
Toes, 80 INDEX. 
125 
Tongue, 68 
Tonsils, 68 
Trachea, 72 
Tragicum, 83 
Truncus arteriosus, 56 
Tympanum, 82 
Umbilical cord, 51 
vesicle, 44 
Urachus, 65 
Ureter, 64 
Urethra, 10, 74, 75 
female, 75 
male, 74 
Urogenital sinus, 64, 72 
Utero-placental circulation, 51 
Uterus, 14, 78 
in pregnancy, 93 
masculinus, 75, 77 
Vagina, 13, 78 
bulb of, 9 
in pregnancy, 94 
Varolian bend, 61 
Vas deferens, 77 
Vasa efferentia, 77 
Veins, cardinal, 57 
ductus Cuvieri, 57 
jugular, 57 
omphalo-mesenteric, 56 
Veins, sinus terminalis, 56 
sinus venosus, 57 
vitelline, 56 
Ventricle, third, 61 
fourth, 62 
Vertebral artery, 56 
Vesicle, blastodermic, 37 
germinal, 29 
Purkinje’s, 29 
umbilical, 44 
Vestibule, 8 
Vestibulum vaginae, 75 
Visceral cleft, 68 
Vitelline duct, 44 
loop, 70 
membrane, 28 
Vitellus, 28 
Vitreous body, 84 
Vulva, 6 
Vulvo-vaginal gland, 9 
Wagner, spot of, 29 
Wharton’s jelly, 51 
Wolffian body, 63 
duct, 63 
ridge, 63 
Yelk, 28 
Zona pellucida, 28-30 August, 1894. 
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