NOTES ON THE 
Larynx and Brain 
BY 
HORACE J WHITACRE 
NEW YORK: 
1894. PREFACE. 
These notes are intended to give the anatomy 
of the brain and larynx as given in the lectures 
of Dr. Huntington, the demonstration of Dr. 
Gallaudet and Dr. Sands. The Brain Anatomy 
of Gray is not always good and the recent book 
of on the Brain is too minute and compli- 
cated for every student to work out. These 
notes are based upon demonstrations and upon 
Quain's recent Anatomy of the Brain, and are 
meant to include the important parts. 
H. J. W. LARYNX. 
The Larynx is the organ of voice placed at the upper 
part of the air passages and situated in the upper median 
neck region. It is composed of cartilages connected by liga- 
ments and moved by intrinsic muscles. 
The Cartilages are the thyroid, cricoid, epiglottis, ary- 
tenoid, cornicula laryngis and cuneiform. 
The Thyroid, is the largest cartilage of the larynx and 
gives to it general shape. It consists of twq quadrangular 
lamellae of cartilage placed vertically, united at an acute 
angle in front, and forming the vertical projection of Adam's 
apple. The outer surface of each lamella presents an ob- 
lique ridge running from a tubercle in front of the root of the 
superior cornu downward and forward to another tubercle 
on the inferior border. This ridge gives attachment to thyro- 
hyoid and sterno-thyroid muscles; the area posterior to the 
ridge gives attachment to a part of the inferior constrictor 
muscle. The inner surface is smooth, concave and gives 
attachment in the angle to epiglottis, true and false cords, 
thyro-arytenoid muscles and crico-thyroid membrane. The 
upper border of the thyroid cartilage is notched in the mid- 
dle line, the incisura. It gives attachment throughout its 
whole extent to the thyro-hyoid membrane. The lower bor- 
der presents the above named tubercle, which marks the 
division line between the straight and oblique parts of the 
crico-thyroid muscle. The crico-thyroid membrane does not 
attach to the lower border but to the inner surface at the 
anterior angle of the cartilage alone. The posterior border 
is thick and terminates above and below in cornua. The 
superior cornua are long, narrow processes directed upward, 
backward and inward, which give attachment at their ex- 
tremities to the lateral thyro-hyoid ligaments. The inferior 
cornua, short and thick, are directed downward, forward 4 
and inward, and present on their inner surfaces oval facets 
for articulation with the tubercles of the cricoid cartilage. 
The posterior border receives the insertion of the stylo- 
pharyngeus and palato-pharyngeus muscles. 
The cricoid cartilage forms the lower and back part of 
the framework of the larynx. The cartilage may be divided 
into a posterior lamina and anterior ring portion with the 
articular tubercles on the side to mark the dividing line. 
The lamina is quite large and forms a posterior wall to the 
cavity. Its posterior surface is divided by a vertical ridge, 
the linea eminens, into two broad depressions, the foveae, 
for the attachment of the crico-arytenoideus posticus muscles. 
Its upper border is surmounted on either side by an oval 
articular facet for the arytenoid cartilages. Between the 
facets is a slight notch giving attachment to a part of the ary - 
tenoideus muscle. The anterior ring portion is narrow, 
convex, smooth and gives attachment superiorly to crico- 
thyroid membrane, externally to the crico-thyroid and 
inferior constrictor muscles. The lower border of the two 
portions of the cartilage are in one horizontal plane and con- 
nected to the upper ring of the trachea by fibrous membrane, 
while the upper border is in a much higher plane behind 
than in front. 
The arytenoids (pitcher-shaped) are two pyramidal 
cartilages resting on the superior border of the lamina of the 
cricoid. Their structure is hyaline cartilage with a point of 
fibro-cartilage which is not to be confused with the cartilage 
of Santorini. Each cartilage presents three surfaces, a base 
and an apex. The antero-external surface is convex, rough 
and gives attachment to the internal thyro-arytenoid muscle. 
In the middle of this surface is a triangular depression to 
which the false vocal cords are attached. Above and below 
this fossa are the superior and inferior tubercles. The pos- 
terior surface is concave for the attachment of the aryte- 
noideus muscle. The internal surface is narrow, plane and 5 
covered with mucous membrane. The base is broad and 
presents a concave articular surface which rests on the cricoid. 
Its external angle or muscular process is rounded, promi- 
nent and extends outward and backward. It received the 
insertion of the external thyro-arytenoid, the posterior and 
lateral crico-arytenoid muscles. The anterior angle or vocal 
process extends directly forward as a prominent pointed 
process which gives attachment to the internal thyro- 
arytenoid muscle and true vocal cords. The apex of the 
arytenoid is pointed, directed backward and inward and sur- 
mounted by the cartilage of Santorini. 
The Cartilages of Santorini, or cornicula laryngis, 
prolong fhe arytenoid cartilages backward, inward and 
downward as conical fibro-cartilaginous nodules. They are 
attached to the arytenoid by fibrous tissue, rarely by an 
articulation. 
The Cartilages of Wrisberg or the cuneiform are 
small, club-shaped nodules of cartilage, which extend oblique- 
ly downward and forward in the posterior part of the aryteno- 
epiglottidean fold. They are roughly parallel to the ary- 
tenoid and the larere, blunt end forms above the nodule seen 
° if 
in the edge of the fold.. 
The epiglottis is a leaf-shaped lamella of fibro-cartilage 
attached by its long, narrow stalk to the receding angle of 
the thyroid cartilage just below the incisura. Its upper 
broad portion is unattached and free to close or open the 
superior aperture of the larynx. The anterior surface is 
curved forward toward the tongue. The reflection of mucous 
membrane from it to the tongue gives rise to a median and 
two lateral folds, the glosso-epiglottidean ligaments and 
two depressions or valleculae between them. The posterioi 
surface is concave from side to side, convex from above 
downward, and studded by a number of pits for the lodg- 
ment of mucous glands. The tubercle is a projection on 6 
the lower part of its posterior surface made by a pad of fat 
anterior to the cartilage. 
The ligaments connecting the larynx with the hyoid 
bone are the thyro-hyoid membrane, the middle and two 
lateral thyro-hyoid ligaments and the hyo-epiglottic liga- 
ment. 
The thyro-hyoid membrane is a double layer of mem- 
branous tissue extending from the upper border of the thy- 
roid cartilage below to the hyoid bone above. The external 
layer of this membrane is thickened cervical fascia and the 
internal is the mucous membrane lining the pharynx. 
The lateral thyro-hyoid ligaments are rounded cords 
passing from the superior cornua of the thyroid to the apices 
of the greater cornua of the hyoid bone. They are included 
between the layers of thyro-hyoid membrane and are not 
thickened portions of it. The cartilago triticea is a small 
cartilaginous nodule that frequently forms in some part of 
this ligament. 
The middle thyro-hyoid ligament is a very thick 
band which is attached below to the median notch in the 
superior border of the thyroid. It passes up behind the body 
of the hyoid bone, separated from it by a bursa, and attaches 
to the upper margin of its posterior surface. Posterior to 
the ligament is a fatty pad which separates it from the epi- 
glottis and gives rise to the tubercle of the latter. 
The hyo-epiglottic ligament is a fibrous band extend- 
ing from the anterior surface of the epiglottis to the upper 
border of the body of the hyoid bone. 
The crico-thyroid membrane is the firm V-shaped 
fibrous lamina connecting these two cartilages. It is 
attached below to the upper border of the cricoid, while 
above it has a single connection to the thyroid in the receding 
angle a little above the lower border. The upper borders of 
the membrane are free and somewhat thickened to form the 
inferior thyro-arytenoid ligaments, which when covered 7 
by mucous membrane, form the true vocal cords. This 
position of the membrane leaves a space on each side between 
it and the inner surface of the thyroid which is arched over 
by a membranous diaphragm from the crico-thyroid mem- 
brane to the lower border of thyroid cartilage. This arch- 
ing membrane separates two muscles; the thyro-arytenoid 
above and the lateral crico-arytenoid below. 
The lateral corniculo-pharyngeal ligaments are two 
small, rounded bands about three-fourths of an inch long, 
which start from the apex of each cornicula laryngis car- 
tilage and run downward and inward to 'converge in the 
median line, and there terminate in the loose tissue of the 
pharynx. The middle crico-pharyngeal ligament is a 
single short, broad band attaching the pharynx to the linea 
eminens. 
The superior thyro-arytenoid ligaments, each of 
which extends from the angle of the thyroid to the trian- 
gular depression on the anterior surface of the arytenoid, are 
not ligaments, but structures of fatty and areolar tissue cov- 
ered by mucous membrane. 
The kerato-cricoid are the articular ligaments of the 
crico-thyroid articulation. They are three in number. The 
anterior, narrow and long, extends downward, forward and 
inward from the inferior cornu of the thyroid cartilage apd 
attaches some distance from the articular surface. / The 
posterior inferior, short and broad, fuses by one edge with 
the preceding. It is attached to the articular edge of the 
thyroid above and the cricoid below. The posterior supe- 
rior is long and runs obliquely upward and inward to the 
lamina of the cricoid tar away from the articular surface and 
under cover of the posterior crico-arytenoid muscle. 
The crico-arytenoid articulation is by a capsular lig- 
ament. 
Movements of the arytenoid. The joint is of the 
reciprocal reception type, formed by two oval surfaces with 8 
their long axes at right angles to each other, that of the 
cricoid being transverse in direction. It permits of motion, 
(1) In an antero-posterior plane; an anterior movement 
relaxing the cords, a posterior movement tightening them. 
(2) In a lateral plane ; motion outward widens and motion 
inward narrows the rima glottis. (3) Rotation about a ver- 
tical axis ; outward rotation widens the glottis and makes 
tense the cords; inward rotation narrows the glottis and 
makes the cords lax. 
The muscles of the larynx are : 
The thyro arytenoideus externus muscle. Origin, 
just external to the median line, low down in the angle of 
the thyroid. Insertion,-transverse part into the muscular 
process and external border of the arytenoid. The oblique 
part sends fibres to epiglottis,superior cord and aryteno-epi- 
glottie fold. Action,-transverse fibres rotate the ary- 
tenoid inward and narrow the glottis ; the oblique fibres 
depress the epiglottis, compress the sacculus laryngis, and 
make the cords tense. 
The thyro-arytenoideus internus. Origin,-directly 
in the angle from the thyroid and from the outer surface of 
the crico-thyroid membrane. Insertion,-vocal process and 
anterior surface of arytenoid. Action,-transverse fibres 
give motion forward of arytenoid, thus loosening the cords, 
and downward rotation of the cricoid when the ligaments of 
the arytenoid become tense. It makes the cord tense by 
means of the ary-vocalis. The oblique fibres compress the 
sacculus. These two thyro-arytenoid muscles are fused at 
their origin, but diverge behind. The inferior thyro-aryte- 
noid does not go above the inferior cords except at the poste- 
rior part. The distribution of the oblique fibres of both to 
the superior cord is found only posteriorly where no sacculus 
exists. The ary-vocalis is a part of the interna] thyro-aryte- 
noid, best shown by diagram. 
The Arytenoideus. Origin,- posterior surface and 9 
outer border of arytenoid. Insertion,-corresponding part 
of opposite side. Action, approximation of the two aryte- 
noid cartilages, thus narrowing the glottis. It is the only 
single muscle of the larynx. It lies underneath the aryteno- 
epiglottic. 
The Aryteno-epiglottideus. Origin,-base of pos- 
terior surface of one arytenoid and a few fibres from the apex 
of the opposite arytenoid as it passes around. Insertion, 
lost in the aryteno-epiglottic fold. Action,-motion inward 
of the arytenoid, depression of the epiglottis, and a narrow- 
ing of the superior aperture of the larynx. The combination 
of the three movements gives a sphincter action. 
The Crico-arytenoideus posticus. Origin,-foveae 
on the posterior surface of the lamina of the cricoid. In- 
sertion, muscular process of Action,-out- 
ward rotation of the arytenoid. 
The Crico-arytenoideus lateralis. Origin,-from the 
lateral surface of the crico-thyroid membrane and the upper 
border of cricoid. Its course is backward and upward. In- 
sertion,-muscular process and external border of arytenoid. 
Action,-inward rotation of the arytenoid. 
The Crico-thyroid rectus. Origin,-cricoid, front and 
lateral portion. Insertion,-the lower border of the thyroid 
as far back as the tubercle. Action,-upward rotation of 
the cricoid. 
The Crico-thyroid obliquus. Origin,-cricoid, lower 
down and farther back than the preceding. Insertion, 
lower border of thyroid behind tubercle and anterior border 
of the inferior cornu of the thyroid. Action,-traction 
backward on the cricoid. The twotparts of the crico-thyroid 
muscles are by far the most important agents in producing 
tension of the vocal cords. The cricoid cartilage is always 
tlie movauTeTthe thyroid, the fixed element. 
That part of the laryngeal cavity included between the 
planes of the false and true cords is known as the ventricle. 10 
From it a pouch is given off, the sacculus laryngis, which 
passes up behind the false cords. It exists only anteriorly. 
A small valve of mucous membrane guards its orifice. 
Inferiorly, the larynx communicates with the trachea by 
a narrow slit between the true cords known as the rima 
glottidis or the glottis. The rima has two portions, (1) an 
intraligamentous or vocal portion, and (2) a posterior intra- 
cartilaginous or respiratory portion, which is never absolutely 
closed. 
The superior aperture of the larynx is made up of 
epiglottis, aryteno-epiglottic folds, cartilages of Wrisburg and 
Santorini, and the interarytenoid fold. The aryteno-epi- 
glottic fold is made up of muscle fibre, areolar tissue and 
fat covered by a mucous membrane. The reflection of mu- 
cous membrane to the inner side of the thyroid cartilage 
creates a depression, the fossa pyriformis. The inter- 
arytenoid folds is of mucous membrane and muscle fibre. 11 
MEDULLA OBLONGATA. 
General shape and position-The medulla oblongata 
is that portion of the cerebro-spinal system which connects 
the cerebral system with the spinal. It is in reality an 
enlarged upper end of the spinal cord, and with some re-ar- 
rangements contains all the elements of the cord. Its length 
is one inch, its greatest breadth three-fourths of an inch, its 
greatest thickness rather less than three-fifths of an inch. 
In shape it is pyramidal, with the apex downward and 
placed arbitrarily at the lower margin of the foramen 
magnum. Ventrally its upper limit or base is sharply 
marked off from the Pons by a deep groove made by the 
lower border of the elevated mass of transverse fibres of the 
Pons. Under these transverse fibres which connect the 
cerebellar hemispheres, the longitudinal fibres of the medulla 
disappear as they pass upward. Ventrally the medulla is 
rounded and rests in the basilar groove of the occipital bone. 
Dorsally it is more flattened and directly continued into the 
Pons, and lies in the fossa between the hemispheres of the 
cerebellum. From its side and anterior surface emerge cer- 
tain cranial nerves, viz : VI to XII. 
Surface Markings. The surface markings of the 
medulla are in general a series of longitudinal columns, 
separated by grooves, each with its counterpart in the cord. 
One groove expands into the fourth ventricle. At the 
upper end, situate laterally, is an ovoid eminence known 
as the olivary body. The anterior and posterior median 
fissures which partially bisect the cord are continued into 
similar fissures in the medulla. The anterior fissure ex- 
tends as far as the Pons, where it ends in a depression, the 
foramen caecum. It is interrupted low down by the 
decussation of the pyramids. The posterior fissure extends 
only as far as the middle of the medulla, where it expands 12 
into the fourth ventricle. Besides the longitudinal fibres of 
the columns, certain transverse fibres emerge from the ante- 
rior and posterior fissures-the arcuate and acoustic fibres. 
The columns in order from the anterior fissure are : 
1. Pyramid. 
2. Lateral Tract (and olive). 
3. Direct Cerebellar tract and Restiform body. 
4. Funiculus of Rolando. 
5. Funiculus Cuneatus. 
6. Funiculus Gracilis. 
The Pyramids appear to be a direct continuation up- 
ward of the anterior columns of the cord, but this is true 
only of a small portion. The main mass is made up of the 
crossed pyramidal bundles which cross the anterior fissure 
from the opposite lateral column, unite with the median part 
of the anterior column of the cord and form the eminence on 
either side of the median line. 
The pyramid is more marked above and is constricted 
at the point where it enters the pons as a single large bundle. 
It is bounded mesially by the anterior fissure, laterally by 
the lateral column and olivary body. From the groove 
between the pyramid and olive the XII nerve emerges. The 
pyramidal bundle soon breaks up into many smaller bundles 
in the Pons and is traced into the corresponding internal 
capsule of the cerebrum. 
The decussation of the pyramids is the name given 
to the obliquely crossing bundles of the lateral pyramidal 
tract which are seen in the anterior median fissure at the 
lower part of the medulla oblongata. The extent of decus- 
sation visible varies much. 
Lateral Tract and Olive. The lateral column of 
the cord appears to be directly continued upward as the 
lateral tract of the medulla which is a short, broad column 
just external to the pyramid, but, as was said above, a large 
part of this lateral column crosses over to form the pyramid. 13 
The tract dips under the lower end of the olive and as it 
does so is crossed by the external arcuate fibres. The 
fibres of this tract are derived from the fundamental fasci- 
culus and anterior radicular zone of the cord. They break 
up into the formatio-recticularis of the medulla. 
The Olive is the eminence occupying the upper part of 
the lateral area and extends from the termination of the 
lateral column almost to the Pons. It is surrounded by a 
well-marked groove. The part of the groove that lies in- 
ternal to it, together with the groove between pyramid and 
lateral tract corresponds in position with the anterior 
nerve roots of the cord. That groove between the olive 
and lateral tract and the restiform body corresponds in posi- 
tion with the posterior nerve roots. The hypoglossal 
nerve emerges from the former; the IX, X and XI nerves 
from the latter groove. 
On the posterior region of the medulla is found, contin- 
uing around in order, the Direct Cerebellar tract, a narrow 
strand of fibres derived from the lateral column of the cord. 
The tract is noted in the cord as a set of obliquely crossing 
fibres which turn upwards as they cross the funiculus of 
Rolando and then appear to blend with this column as well 
as with the funiculus cuneatus. They do not really blend how- 
ever, but are reinforced by a large number of fibres from the 
opposite side of the medulla-the external and internal arcu- 
ate fibres-and the whole mass so produced, forms the 
rounded, prominent restiform (rope like) body which passes 
directly into the corresponding cerebellar hemisphere and 
forms its inferior peduncle. 
Restiform body consists of: Direct cerebellar tract; 
external arcuate fibres; internal arcuate fibres. 
The Funiculus of Rolando is a longitudinal promi- 
nence between the direct cerebellar and cuneate columns, 
caused by the projection toward the surface of the grey mat- 
ter of the posterior horn (or Substantia Gelatinosa of Rolan- 14 
do.) It is narrow below and broadens as the considerable 
eminence of the Tubercle of Rolando is reached. It differs 
from the other columns in not being caused by longitudinal 
white fibres. 
Funiculus Cuneatus. The column of Burdach, situ- 
ated in the posterior region of the cord, is continued into the 
medulla as the funiculus cuneatus. This, like the funiculus 
gracilis, expands as it passes up, and opposite the clava of 
the funiculus gracilis presents an enlargement, best marked in 
children, the cuneate tubercle. From this point it dimin- 
ishes in size until it reaches the upper part of the medulla, 
where the fibres dip down to its own nucleus and end there. 
From these nuclei, however, separate fibres start, viz.: those 
composing the fillet. 
Lastly, those columns on either side of the posterior me- 
dian fissure, the funiculi Graciles, represent the continuation 
upward of the tracts of Goll in the cord. Each funiculus is 
well marked, especially so as the fourth ventricle is reached 
where it broadens out into an expansion known as the clava. 
As the ventricle opens out the davse diverge and form the 
lateral boundaries of the ventricle in its lower part. Above, 
the clavae are tapered off and soon become no longer trace- 
able. The fibres of this column like the cuneate, dip down 
to a distinct nucleus gracilis, which, together with the cune- 
ate nucleus, sends out the fillet. Funiculus Gracilis and 
Cuneatus do not enter the restiform body. The clava 
and cuneate tubercle are each formed by the projection out- 
ward at this point of the considerable mass of the respective 
nuclei. 
Fourth Ventricle. The fourth ventricle is the space 
into which the central canal of the cord expands superiority. 
It is a space between the medulla and pons anteriorly, and 
the cerebellum behind. It is diamond shape, or may be 
said to be formed of two triangles with coincident bases. 
The lower part appears to be formed by the divergence at 15 
an acute angle of the funiculi cuneati et graciles. Supe- 
riorly the boundaries are formed by the convergence of the 
superior peduncles of the cerebellum, narrowing the ventri- 
cle down again to a point in the aqueduct of Sylvius. To 
the pointed lower triangle is given the name calamus scrip- 
torius, from its resemblance to the reed pen of the ancients. 
Opposite the middle peduncle of the cerebellum, the ventri- 
cle has obtained its greatest width, and at this point certain 
prolongations of the space are found. These are known as 
the lateral recesses which run out laterally, wrap around 
the inferior peduncles and extend on either side as far as the 
flocculus. The recess is roofed by the inferior medullary 
velum and tela choroidea inferior, bounded anteriorly by 
the inferior peduncle and limited below by the ligula. The 
lateral angle of the ventricle is the point of junction of the 
three peduncles, and is not to be confounded with the lateral 
recess. 
The Lateral Boundaries of the fourth ventricle are 
formed inferiorly on either side by the clava of funiculus 
gracilis, funiculus cuneatus and restiform body. In the 
upper half the superior peduncles form the boundaries as 
they converge from a widely separated position to a point of 
contact. By such a course they pass gradually to the roof 
of the ventricle as they go upwards. 
Roof.-Superiorly the triangular interval between the 
two peduncles is bridged over by a lamina of white matter 
marked across with grey streaks. This is the superior me- 
dullary velum, or valve of Vieussens, and with the pe- 
duncles, forms the roof of this part of the ventricle. On the 
dorsal surface of the valve are found transverse grey laminae 
which together form the lingula of the worm. These 
laminae are continued laterally into the cerebellum as the 
frsenula. The white matter of the valve is directly con- 
tinued into that of the cerebellum. The superior velum as a 
whole meets with the inferior velum from below to form the 16 
tent which may be designated as the roof of the central por- 
tion of the ventricle. In the lower one-half the roof is 
formed in part by the inferior medullary velum, a pro- 
jection of white matter analogous to the superior velum. 
The velum connects the nodule of the cerebellar worm with 
the flocculus of the lateral hemispheres. It ends abruptly 
below in a thickened edge to which is attached the telacho- 
roidea inferior which completes the roof of the ventricle. 
Tela choroidea inferior, is a double layer of pia mater 
covered on its anterior or ventricular surface by a single lay- 
er of epithelium, which bridges over the triangular interval 
between the inferior peduncles of the cerebellum. The ana- 
tomical specimen will show the inferior medullary velum with 
an inferior free edge, and the fourth ventricle open. This is, 
however, not normal, but the result of tearing away this 
double layer of pia from its attachment to the lower edge of 
the velum and necessarily with it the layer of epithelium. 
These two folds of pia were originally separate, the one on 
the inferior surface of the cerebellum, the other on the su- 
perior surface of the roof of the fourth ventricle-a sort of 
pocket, but they have fallen together and fused to an extent. 
The epithelium needs explanation. It is the result of 
a thinning of true brain tissue, wdiich at this point has 
gone on to such an extent that but a single layer of cells is 
left. It is none the less true brain tissue and the central 
canal or ventricular system is not open at this point. The 
statement, however, is made that there is a small hole termed 
the foramen of Majendie in the tela, a little above the 
point where the central canal of the cord expands into the 
fourth ventricle. 
Laterally, the roof epithelium is thickened by white ner- 
vous matter before becoming continuous with that of the 
floor, and when the roof epithelium is torn off, a ragged, 
slightly prominent membrane, the ligula (or taenia) remains 
attached to the surface of the medulla as a result of the 17 
thickening. The ligula commences at the apex of the clava, 
follows the lateral boundary of the ventricle and then turns 
out to form the inferior boundary of the lateral recess. An- 
other thickening of the roof at the apex of the ventricle is 
known as the Obex. 
From the roof project two longitudinal vascular infold- 
ings of pia on either side of the median line, known as the 
choroid plexus. They are everywhere covered by epithe- 
lium. Prolongations of the plexus extend into the lateral 
recess, from the apex of which they emerge encircled by'the 
ligula, which at this point is known as the Cornucopia. 
Floor.-The floor of the fourth ventricle is made up of 
medulla for its lower half and pons for its upper half. The 
point of division between the two corresponds to the tent 
and to the widest part of the ventricle. This line of demar- 
cation is indicated on the surface by the acoustic strise, white 
fibres crossing transversely the grey matter of the floor. 
These fibres begin in the ventral part of the medulla, emerge 
from the posterior raphe, curve outward over the restiform 
body and pass not to the lateral root of the eighth cranial 
nerve as is often stated, but very largely to the Flocculus. 
An aberrant bundle often passes into the middle cerebellar 
peduncle. 
The floor of the ventricle is bisected by a median longi- 
tudinal groove on either side of which is a ridge, the funi- 
culus teres, extending throughout its whole length. The 
funiculus teres represents the small remaining portion of the 
base of the anterior cornu which in the cord was ventro- 
lateral to the canal but now comes to the surface in the floor 
of the canal as it opens out. Immediately below the medul- 
lary or acoustic strise is a triangular depression-the inferior 
fovea. From its apex at the strise, one groove runs down- 
ward and inward to the apex of calamus scriptorius, thus 
cutting off a triangular prominent area with base upward 
(a part of funiculus teres) known as the trigonum hypo- 18 
glossi. Another groove passes downward and outward to 
the lateral boundary of the ventricle marking off another 
prominent triangular area, the trigonum acoustici. The 
remaining triangular area with its apex at the inferior fovea 
is known as the ala cinerea. Its depressed upper part forma 
the inferior fovea and its lower prominent part the emi- 
nentia cinerea. The latter contains the nuclei of IX and 
X nerves. Above the acoustic striae the floor of the ventri- 
cle is marked in the middle of each lateral half by a distinct 
angular depression, the superior fovea. The superior fovea 
is in a line with the inferior fovea and separated from it by an 
eminence over which the acoustic striae pass. Between the 
fovea and the median groove is the upper part of funiculus 
teres. A shallow depression extends from the apex of the 
superior fovea up toward the aqueduct of Sylvius. This 
groove is known as the locus coeruleus and is rendered 
dark colored by the pigment known as the substantia fer- 
ruginea. 
TABULATED BOUNDARIES. 
ROOF. 
LATERAL. 
FLOOR. 
Upper 
Half. 
Sup. Med. Velum, 
(or Vieussens.) 
Sup. Peduncles of 
Cerebellum. 
Sup. Peduncles of 
Cerebellum. 
Pons. 
Central 
Part. 
Tent of Cerebel- 
lum. 
Lateral angle or 
junction of the 
three peduncles. 
Lateral Recess- 
(1) Inf. Velum. 
(2) Pia Mater. 
(3) Peduncle of - 
Cerebellum. 
(4) Ligula. ✓ 
Junction of Pons 
and Medulla. 
Lower 
Half. 
Tela Choroidea 
Inferior. 
Inf. Medullary 
Velum. 
Choroid Plexus. 
Inf. Peduncles of 
Cerebellum. 
Upper ends of- 
(1) Funiculus 
cuneatus. 
(2) Clavae of 
gracilis. 
Medulla. 19 
Internal Structure.-The first great change in trans- 
ition from cord to medulla is made by the passage of the 
fibres of the crossed pyramidal tract through the anterior 
horn of grey substance across the median line to the oppo- 
site side. By this process the grey matter is broken up and 
interspersed through the fibres to constitute the formatio 
reticularis. The double process of a shifting laterally 
of the posterior horns and the enlargement of the posterior 
columns of the cord has caused such an arrangement that 
viewing the system in section the horns have come to assume 
a position almost at right angles to the median fissure, in- 
stead of continuing, as in their position in the cord, to make 
an acute angle with it. The tip of the posterior horn en- 
larges and conies close to the surface, where it produces the 
projection of the funiculus of Rolando. A little higher up 
the horn swells into the tubercle of Rolando. Numerous 
collections of grey matter throughout the medulla represent 
the nuclei of various nerves and special bundles. 
The Formatio Reticularis occupies the whole of the 
anterior and lateral mass dorsal to the olives and pyramids. 
The reticular appearance is given by the intersection of lon- 
gitudinal and transverse bundles. The longitudinal fibres 
are made up of the fibres from the antero-lateral columns, 
by a special bundle from the antero-lateral column known as 
the posterior longitudinal bundle, and by the fillet. Or the 
longitudinal fibres may be said to be made up of the lateral 
area of the cord after the crossed pyramidal and direct cere- 
bellar tracts have been taken out. The transverse fibres 
pass (1) obliquely from the raphe outward in rather a curved 
course to the nuclei of gracilis and cuneatus as the large 
internal arcuate fibres, (2) between the two olives as the 
olivary peduncle, (3) from the raphe to the restiform bod- 
ies as the small internal arcuate fibres. In some parts 
grey matter with nerve cells enters into the formatio reticu- 20 
laris. The cells are especially large and numerous in the 
lateral area, and mostly absent in the antero-mesial portion. 
The Raphe of the medulla consists of fibres running 
dorso-ventrally, longitudinally and across the septum more 
or less obliquely, intermingled with a number of nerve cells 
of grey matter. The dorso-ventral fibres are continuous 
ventrally with the external arcuate fibres, dorsally with 
the acoustic striae. The longitudinal fibres consist of the 
dorso-ventral fibres that have changed direction, and the 
internal arcuate fibres. The oblique fibres comprise those 
internal arcuate fibres which form the fillet, the fibres of the 
olivary peduncle, and certain cranial nerve fibres. The raphe 
is continued up into the dorsal portion of the pons. 
Nuclei.-The various cranial nerve origins are indicated 
in the floor of the fourth ventricle by diagram. Among the 
larger collections of grey matter are the nuclei of funiculus 
gracilis, cuneatus and the olive. 
The nuclei of funiculus gracilis and cuneatus indi- 
cate a considerable increase in the grey matter at the base of 
the posterior horn of the cord as we pass upward. The 
nuclei are at first narrow, but as the canal opens out they 
become quite thick masses which produce externally the 
eminences of the clava and cuneate tubercle. The fibres of 
the corresponding columns dip down to end in these nuclei. 
Separate fibres, the internal arcuate, emanate from the 
nuclei, sweep forward and inward in a curved manner to the 
raphe. These intercross with those of the opposite side in a 
decussation somewhat higher up than that of the pyramids 
and form on either side a considerable bundle of fibres known 
as the fillet which lies just dorsal to the pyramid. 
The nucleus of the olive is a portion of grey matter 
not traceable from the grey matter of the cord. The grey 
matter is not visible from the surface, but is covered by 
longitudinal and transverse white fibres in a sort of capsule. 
Its arrangement is that of a thin wavy lamina of grey sub- 21 
stance forming a continuous capsule, except on its inner or 
median surface, where the hilum receives the considerable 
tract of white fibres of the olivary peduncle. This ema- 
nates from the raphe, and is derived from the opposite olive. 
The fibres of this peduncle diverge as they enter the hilum 
of the olive; some pass to the grey lamina, but the majority 
pass in small bundles through the lamina. Those which are 
more posterior turn backwards and course obliquely through 
the posterior part of the lateral area of the medulla to the 
restiform body as the internal arcuate fibres. These are 
to be distinguished by their small size from the internal 
arcuate fibres forming the root of the fillet. The other more 
anterior fibres of the olivary peduncle, after piercing the 
lamina reach the surface of the olive, where they form a part 
of the external arcuate fibres and are continued into the 
restiform body. Through the"restiform body, arched fibres, 
and peduncle of the olives, the cerebellar hemisphere of one 
side is connected with the olive of the opposite side. The 
opposite olive atrophies on destruction of a cerebellar hemis- 
phere. The olivary nucleus is connected, however, with the 
cerebral hemisphere of the same side. Tt has no direct con- 
nection with the cord. 
Arcuate fibres. Of these there are three sets, one ex- 
ternal and two deep. The external or superficial arcuate 
fibres emerge for the most part from the anterior median fis- 
sure, pass over the pyramids and olive, through the groove be- 
tween the lateral tract and lower end of the olive to enter 
into the formation of the restiform body. In the region of 
the olive these fibres are joined by those described above, as 
passing through the grey lamina of the olive. Traced back 
into the anterior median fissure they are seen to enter the 
raphe, cross over in it and are then supposed to become 
longitudinal. Their further course is not known. Of the 
internal arcuate fibres there are two sets. First, those 
described as formed by the fibres of the olivary peduncle 22 
which pierce the grey lamina of the olive, course through the 
substance of the medulla, and join the restiform body. Sec- 
ond, the larger set also described as beginning in the cuneati 
et graciles nuclei, coursing obliquely forwards and inwards to 
the raphe and then crossing over to the opposite side in a 
decussation to form the fillet of the opposite side. 
PONS. 
Pons.-The Pons Varolii forms a prominence marked 
by transverse fibres, above and in front of the medulla and 
between the hemispheres of the cerebellum. At the sides the 
transverse fibres are collected into a compact mass which 
enters the cerebellum as its middle peduncle. The ventral 
surface of the pons projects beyond the level of the other 
parts, is of quadrilateral form, and rests upon the sphenoid 
and basilar process of the occipital bone. The surface is 
marked by a longitudinal median groove which receives the 
basilar artery. This groove is in a measure due to the pas- 
sage upward of the fibres of the pyramids of the medulla on 
either side of the median line and covered in by the trans- 
verse fibres of the pons. The dorsal surface forms a part of 
the floor of the fourth ventricle. 
Internal Structure.-The ventral portion consists of 
longitudinal and transverse fibres interlacing and arranged 
in layers. The posterior or dorsal portion is a continuation 
upward of the reticular formation and grey matter of the 
medulla. There exists in the pons a median raphe or 
septum similar in structure to that of the medulla, but which 
does not extend through the ventral half because of the 
transverse and oblique fibres in this region. 
Besides the grey matter freely interspersed through its 
formatio recticularis, the pons has two main collections, viz : 
the superior olivary nucleus and nucleus of the seventh 23 
cranial nerve. Minor collections represent a part of fifth 
cranial nerve nucleus. The superior olivary nucleus is 
a collection of grey nerve cells situated in the lower part 
of the pons near the medula, and lying dorsal to the pyra- 
midal fibres. Their connections are little understood at 
present, but enclosing and in definite connection with some 
of its cells is a transverse bundle of fibres, the trapezium. 
This bundle curves around these nuclei, runs out over the 
seventh nerve roots and is connected with the accessory 
auditory nucleus and ventral root of the eighth nerve. 
Therefore the trapezium forms a cerebral commissure for the 
nuclei of the VIII nerves. 
Fibres of Cord Traced. 
The Posterior columns form in the medulla the funi- 
culi cuneati et graciles which terminate in their own nuclei. 
From these nuclei emerge certain deep arched fibres which 
pass to the raphe, cross over and pass up as fillet to end partly 
in corpora quadrigemina, partly in cerebrum. Some fibres, 
especially from cuneate nucleus, pass directly into the resti- 
form body of the same side. 
The Lateral column of the cord in large part, namely, 
the crossed pyramidal tract, passes over to form the opposite 
pyramid of the medulla. From here it proceeds in the ven- 
tral part of the medulla and pons to the middle third of the 
crusta, and reaches the cerebral cortex through the internal 
capsule. Some fibres of the pyramid emerge from the ante- 
rior median fissure of the medulla as the external arcuate 
fibres' and then pass to the cerebellum in the restiform body. 
The direct cerebellar tract passes upward at about the 
middle of the medulla, to form a part of the restiform body, 
and terminates in the cerebellar worm. The ascending 
antero-lateral tract passes into the upper part of the pons 
and then turning at about the level of the point of emer- 24 
gence of the fifth nerve, curves backward and enters the 
cerebellum in the superior peduncles and in the valve of 
Vieussens. 
The rest of the lateral column enters into the structure 
of formatio reticularis. Some of its fibres also contribute to 
the fillet, because this is not wholly made up of the fibres 
from the nuclei of the posterior columns, the accession being 
of fibres from the posterior horn of the cord that have crossed 
over in the anterior commissure of the cord, and then 
ascended in the antero-lateral column. 
The anterior column of the cord is in part continued 
into the corresponding pyramid of the medulla, but the major 
part of it dips under the pyramid and forms the longitudinal 
fibres of the formatio reticularis. One bundle of these fibres 
appears quite distinct and definite in the pons, and is known 
as the posterior longitudinal bundle. Other fibres of the 
column join the fillet. 
CEREBELLUM. 
The Cerebellum occupies the posterior fossa of the 
cranium, and consists of two lateral hemispheres joined to- 
gether by a median portion called the worm. The worm 
appears as a well marked prominence in a deep hollow and 
divided by the great transverse fissure into a superior 
and an inferior worm (the latter the most marked). In birds 
and animals of a lower type the worm alone exists. The 
median portion lies behind the fourth ventricle and below 
and behind the corpora quadrigemina from which it seems 
to be suspended by the superior peduncles of the cerebellum. 
Below the cerebellum receives its inferior peduncles from the 
medulla, while in front and at the sides the mass of the middle 
peduncle passes from the pons to the hemispheres. Super- 
iorly the hemispheres are somewhat flattened with a ridge in 25 
the middle from which it slopes laterally and backward. 
Inferiorly the hemispheres are rounded and separated by a 
deep groove, the vallecula, which receives the medulla. 
The cerebellum is characterized by its laminated ap- 
pearance being everywhere marked by deep, closely set 
transverse or curved fissures. Its structure is best demon- 
strated by sagittal sections. 
The great horizontal fissure is the most conspicuous 
fissure. It divides the cerebellum into an upper and lower 
portion, corresponding to the upper and lower surfaces, each 
portion being again subdivided by fissures into lobes. The 
fissure begins on either side at the middle peduncles, extends 
around the outer and posterior border of either hemisphere 
and dips down into the posterior notch. 
The Upper Surface is composed of worm and hemi- 
sphere, each subdivided into lobes by transverse fissures and 
each part of the worm having a corresponding part in the 
hemisphere with which it is definitely connected. Thus we 
have in order from before backwards: 
Worm. 
Hemisphere. 
Lingula, 
Lobulus Centralis, 
Cui men, 
Declive, 
Folium Cacuminis. 
Fraenulum, 
Ala, 
Anterior Crescentic, 
Posterior Crescentic, 
Posterior Superior or Sup. 
Semilunar. 
Lingula.-The lingula is the most anterior lobe of the 
worm and is generally not extended to the hemispheres. It 
consists-of a tongue-shaped group of four or five transverse 
laminae which lie directly on the dorsal surface of the valve 
of Vieussens. If the other lobes may be called bipenniform 
this will be penniform and the white stalk will correspond to 
the valve of Vieussens. When the lobe extends laterally to 
the hemisphere it is known as the fraenulum. 26 
The Lobulus Centralis, the next lobe in order, is con- 
cealed by the culmen. In the natural position of parts the 
primary branch of the arbor vitae to it passes forward and 
upward. The lobe is prolonged into the hemisphere as the 
ala,-a narrow, wing-like strip along the upper and anterior 
part of the hemisphere. 
The Culmen occupies rather more than one-half of the 
upper surface of the worm and constitutes its most prominent 
part. It is marked by several secondary transverse laminae 
and is separated from the declive by a very deep sulcus ex- 
tending to the middle of the organ. The lateral prolonga- 
tion, the anterior crescentic lobe, likewise makes the main 
subdivision of the upper surface of the hemisphere. It is 
marked off by well defined sulci. The culmen receives a 
single stem of the arbor vitae, while the anterior crescentic 
lobe receives three branches from the medullary centre of the 
hemisphere. 
The Declive is another considerable group of well 
marked laminae which form the descending slope of the 
upper surface. The lateral extension of the lobe in the hemi- 
sphere is known as the posterior crescentic lobe which 
together with the anterior crescentic forms the quadrate 
lobe. 
The Folium Cacuminis is formed by the apex of the 
main horizontal stem of the arbor vitae, as a single primary 
folium. It is limited behind by the great transverse fis- 
sure. As the folium passes into the hemisphere it rapidly 
expands with the divergence of the limiting fissures and the 
development of numerous secondary and tertiary folia into 
the posterior superior lobe. Its expansion occurs mainly 
above the horizontal plane and occupies the posterior one- 
third of the upper surface. 
Under surface. The under surface of the cerebellum 
presents more complexity and the correspondence of parts in 27 
the worm and hemispheres is less definite and regular than in 
the superior worm. From before backward we have: 
Worm. 
Hemisphere. 
Nodulus, 
Uvula, 
Pyramid, 
Tuber Valvulae. 
Flocculus, 
Tonsil, 
Digastric, 
Slender and Inf r Semilunar. 
It is sufficient to say that each lobe is marked off by deep 
fissures. 
The Nodulus occupies much the same position relatively 
to the inferior medullary velum and tent that the lingula oc- 
cupies with respect to the superior velum. It is, however, 
better developed as a distinct prominence with a separate 
branch from the arbor vitae. In the natural position of the 
parts it is concealed by the uvula and can not be seen. The 
nodulus is connected with the flocculus, its corresponding 
part in the hemisphere, by the inferior medullary velum. 
This lobe, the flocculus, consists of a collection of lamellae 
diverging from a stalk and situated in the groove between 
the digastric lobe and the middle peduncle of the cerebellum. 
The Uvula forms a considerable portion of the inferior 
worm. It is elongated from before backward, least prominent 
next the nodule and increasingly so up to the pyramid. It is 
purely a mesial structure, separated from the hemispheres by 
deep grooves. At the bottom of the groove is a low, corru- 
gated, grayish ridge, the furrowed band, which connects 
the uvula with the stalk of the tonsil, its corresponding part 
in the hemisphere. The tonsil is a rounded mass of sagittal 
laminae lodged in a depression at the front of the vallecula. 
It is bounded mesially by the uvula, laterally by the digas- 
tric lobe. 
The Pyramid forms the most marked prominence of the 
lower worm, as a long, clavate projection attached to the stem 
of the arbor vitae by a very narrow stalk. It is separated 28 
from the uvula and tuber valvulae by deep fissures and con- 
nected to its large corresponding lobe of the hemisphere by 
a low narrow ridge analogous to the furrowed band. The 
digastric lobe is triangular in shape, with the apex of the 
triangle pointing backward and inward to the pyramid. It 
is generally subdivided by a sulcus. 
The Tuber Valvulae is the hindermost division of the 
worm, between the pyramid in front and folium cacuminus 
behind. It is separated from the latter by the great trans- 
verse fissure. The lateral prolongation broadens out rapidly 
and is represented by two well marked lobes. The semilu- 
nar lobe appears to be in direct continuity. The slender 
lobe next to the great transverse fissure seems to be interpo- 
lated with no corresponding part in the worm. These two 
lobes occupy two-thirds of the inferior surface of the hemi- 
sphere, the greater part of the remaining area being taken 
up by the digastric lobe. 
Arbor Vitae. This term is applied to the appearance 
presented by a sagittal section through the worm. The 
tree-like appearance is due to the fact that we have primary 
laminae giving off secondary, and these in turn beset by ter- 
tiary laminae, the whole covered by a uniform layer of grey 
matter. The stem or corpus trapezoides, is formed by 
the fusion of the superior and inferior medullary velum at the 
apex of the tent. The term arbor vitae applies strictly only 
to the worm. The white matter of the hemispheres is 
much less regularly arranged and forms a central white mass, 
the result of the entrance of the three peduncles. Enclosed 
within its substance is the dentate nucleus a plicated cap- 
sule of compact, yellowish-brown substance, enclosing white 
matter in its interior. The nucleus is open at its anterior 
and mesial part, where it receives the superior peduncles of 
the cerebellum. 
The peduncles of the cerebellum are bundles of fibres 
connecting this with the other parts of the brain. They con- 29 
verge from three directions at the anterior termination of the 
great transverse fissure to make up the medullary white por- 
tion of the hemisphere and ultimately reach the grey cortical 
cells. 
The Superior Peduncles, from which the cerebellum 
seems suspended, emerge from the upper and central part of 
each hemisphere, run forward first on the side, then in the 
roof of the fourth ventricle, and disappear under the corpora 
quadrigemina. The fibres of the superior peduncle emerge 
almost entirely from the hilum of the dentate nucleus. Some 
are traced to the grey lamina of the nucleus, others through 
it to the cortex. Those fibres that do not enter the hilum 
curve around the nucleus. Traced forwards the fibres decus- 
sate under the posterior pair of corpora quadrigemina and 
form a distinct w'hite longitudinal bundle of the tegmentum. 
This bundle encloses a collection of pigmented cells known 
as the red nucleus, receives accessions from these cells and 
is continued into the ventral part of the optic thalamus. 
Certain fibres pass around the optic thalamus into the cere- 
brum while certain other fibres do not decussate but pass 
into the red nucleus of the same side. 
The Middle Peduncle consists of transverse fibres of 
the pons entering laterally the cerebellar hemispheres in two 
thick masses. Some of the fibres traced ventrally end in the 
grey cells of the pons ; others take a longitudinal direction 
in the raphe, or in the fillet and the posterior longitudinal 
bundle of the same side ; a few pass to the opposite cerebellar 
hemisphere. After extirpation of one cerebellar hemisphere 
the degenerations are in the middle peduncle as far as the 
median line, the grey matter of the pons of the same side, the 
fillet and posterior longitudinal bundle of the same side. 
The Inferior Peduncle issues from the lateral hemi- 
sphere between the other two and passes forward immediate- 
ly outside the superior peduncles to reach the lateral wall of 30 
the fourth ventricle. Here it suddenly turns downward at 
right angles, to become the restiform body of the medulla. 
The peduncle is made up of (1) the direct cerebellar 
tract of the cord (2) the external arcuate fibres (3) the internal 
arcuate fibres (4) the fibres of the descending cerebellar tract. 
MID=BRAIN. 
The parts of the brain included under this division are 
all covered by the hemispheres. They are the corpora quad- 
ri gemina, aqueduct of Sylvius, crusta, tegmentum, brachia, 
substantia nigra and internal geniculate body. It serves as 
the connecting band between the cerebral and cerebellar 
hemispheres. In general shape it is a very short and chunky 
rhomboid, with very thick walls as compared to the cavity. 
Nearer its lower surface the rhomb is divided by a lamina of 
grey matter, convex downwards - the substantia nigra. 
All above the lamina is known as tegmentum, all below as 
crusta. 
The superior surface of the mid-brain presents at its 
back part two pairs of rounded bodies, the corpora quadri- 
gemina. Each body is marked off by grooves, the pineal 
gland resting in the groove between the anterior pair. On 
the lateral surface of the mid-brain is seen a well-marked 
groove, the lateral sulcus, which indicates the line of 
division between tegmentum and crusta-the line of outcrop 
of substantia nigra. Crossing obliquely from above down- 
wards and forwards, with the corpora quadrigemina as an 
origin, are distinct bands, the anterior and posterior 
brachia. The posterior brachium passes to the internal 
geniculate body, a prominence of the mid-brain located a 
little farther forward, while the anterior brachium passes 
between this body and the external geniculate, which is 
adjacent to it, but belongs to the optic thalamus and joins 31 
the optic tract. The posterior brachium in its course marks 
oft' a triangular area, bounded by brachium, lateral groove 
and anterior border of pons, where alone the fillet (lower) 
appears on the surface of the brain. Inferiorly the crusta 
are seen as rounded bundles of white matter, which rapidly 
diverge and soon disappear under the cerebral hemispheres. 
They include between them the interpeduncular space, filled 
in posteriorly by the out-cropping of the substantia nigra, 
known here as the posterior perforated lamina, and by 
the corpora albicantia. At the point of divergence is seen 
the emergence of the third cranial nerve. 
The aqueduct of Sylvius is the central cavity of this 
part of the brain, continuous below with the fourth ventricle, 
above with the third ventricle. Its length is rather more 
than one-half inch. Its shape varies in different parts; 
T-shaped on section below, triangular above and an elon- 
gated oval in the intermediary portion. Wholly within the 
tegmentum and near its upper surface, it forms a narrow 
canal, lined by a ciliated epithelium and surrounded 
by a layer of grey matter two or three mm. thick, which is a 
prolongation upward of the grey matter of the floor of the 
fourth ventricle and gives origin to important nerves, viz., 
third, fourth, fifth. 
The crura cerebri correspond to tegmentum-]- crusta-f- 
substantia nigra, i. e., another name for the mid-brain. 
The Crusta are seen on the ventral surface of the mid- 
brain as two longitudinal bundles of fibres, which emerge 
from beneath the transverse fibres of the pons, pass forward 
and outward around the outer side of the optic thalamus, 
and in a large measure enter into the formation of the inter- 
nal capsule. On section they are semilunar in shape and 
receive in their substance the projections of the substantia 
nigra on the concave surface. They consist in the main of 
the prolongation of the longitudinal fibres found in the pons 
and medulla. The crusta maybe roughly divided into three 32 
parts, viz., an outer, middle and inner third. The pyramidal 
tract of the medulla and pons occupies the middle third, 
passes on through the middle portion of the internal capsule 
to the fronto-Rolandic region. This is, therefore, the motor 
element of the crusta. The outer third is sensory, and 
appears in a prominent ridge, laterally known as the curved 
sensory tract. The fibres are traceable downwards to the 
lateral longitudinal bundles of the pons, where they end 
perhaps in grey nuclei, upwards to the posterior part of the 
internal capsule and, consequently, to the occipito-temporal 
cortex. The inner third contains (1) fibres passing to the 
prefrontal cortex through the anterior part of the internal 
capsule, not traceable downwards, and (2) the fibres of the 
mesial fillet, traceable to the corpus striatum and lenticular 
nucleus. 
The Tegmentum includes the corpora quadrigemina, 
posterior longitudinal bundle, fillet, red nucleus and aqueduct 
of Sylvius. It is a continuation upward of formatio reticu- 
laris, with the addition of much grey matter and white fibres. 
A cross section shows its general shape. As it passes for- 
ward it gets thinner (well shown in longitudinal section) and 
finally divides into two lateral parts, which pass into the 
ventral portion of each optic thalamus and form the sub- 
thalamic region. The posterior longitudinal bundle is 
made up of certain longitudinal fibres of the anterior area of 
the cord, which instead of breaking up into the reticular forma- 
tion of the medulla, remain distinct, and become collected in 
the upper part of the medulla into a compact bundle. This 
bundle passes through the pons as a distinct fasciculus, and 
receives here some of those fibres of the middle peduncle of 
the cerebellum which have become longitudinal. It is con- 
nected with the nucleus of the third nerve of the same and 
of the opposite side in passing through the mid-brain, and 
forms, at the posterior part of the third ventricle, the greater 33 
part of the posterior commissure. It finally passes through 
the optic thalamus into the white matter of the cerebrum. 
The Fillet takes origin in the medulla, principally from 
the nucleus cuneatus and gracilis of the opposite side. From 
these nuclei the fibres under the name of the internal arcu- 
ate fibres curve forward and inward to the median raphe, 
decussate with the fibres of the opposite side and form a con- 
siderable bundle on either side of the median line just dorsal 
to the pyramids. It is here, after the decussation, that the 
fibres take the name, fillet. A few fibres derived from the 
posterior horn, and traced through the antero-lateral tract of 
the cord, contribute to the fillet. The bundle passes up 
through the pons and divides into three parts, a mesial, an 
upper and a lower fillet. The mesial fillet, described above, 
remains in the ventral position, forming the inner third of the 
crusta, and is continued on through the subthalamic region 
into the lenticular nucleus. The lower fillet runs obliquely 
outward and appears on the lateral surface of the tegmen- 
tum in the triangular area, above described, as it curves 
upward, then passes principally to the lower corpora quadri- 
gemina. This part receives fibres from the antero-lateral 
tract of the cord through the superior medullary velum. The 
upper fillet, as it passes through the tegmentum, decussates 
with the lower fillet and superior peduncle of the cerebellum 
in the roof of the aqueduct of Sylvius to form the white 
lamina. It passes principally to the upper corpus, but some 
fibres extend through the subthalamic region to the occipital 
region of the cerebrum. 
The Red Nucleus is a cylindrical tract of grey matter 
on either side, located ventrally in the tegmentum. It con- 
sists, essentially, of a number of large, pigmented, grey cells, 
enclosed in the tract of the superior cerebellar peduncle. 
The Substantia Nigra is a curved lamina of grey mat- 
ter, characterized by very darkly pigmented nerve cells, 
which separates the crusta from the tegmentum. It is thicker 34 
mesially than laterally, convex downward, and from the con- 
vex side sends projections into the crusta. Commencing at 
the upper margin of the pons, it extends only as far as the 
corpora albicantia. When the crusta diverge this lamina con- 
tinues complete, except for small perforations, and bridges 
over the space intervening between them as the posterior 
perforated lamina. 
The Corpora Quadrigemina are two pairs of rounded 
eminences, composed mainly of grey matter, situated on the 
dorsal surface of the mid-brain. The upper pair are broader, 
longer and darker in color, but less prominent than the 
lower. Laterally they are not bounded by distinct grooves, 
but are continued as distinct white tracts known as the bra- 
chia. The anterior brachium from the upper corpus passes 
outward and forward between the two corpora geniculata as 
a narrow, twisted band to form one root of the optic tract. 
The posterior brachium from the lower corpus loses itself 
under the internal geniculate body on the side of the mid- 
brain. Some of its fibres pass on under the geniculate body 
to join the optic tract as the commissural fibres of Gudden, but 
they are strictly commissural with the corresponding body of 
the other side and have nothing to do with sight, because : (1), 
after extirpation of an eye the anterior brachium atrophies, 
but the posterior does not; (2), in the mole the posterior bra- 
chium is present, but the anterior is not. 
The lower corpora are made up entirely of grey matter, 
forming two nuclei connected by commissural fibres. They 
are separated from the aqueduct of Sylvius by the white lamina 
alone. The bodies seem to be the termination of the fibres 
of the lower fillet, and as these fibres become continuous in 
part with those of the trapezium, which again is connected to 
the principal auditory nuclei, we must believe a close con- 
nection between the lower corpora and the auditory nerve. 
The upper corpora are larger and less prominent, and 
have a much more complicated structure. In a general way, 35 
we may say that the fibres of the upper fillet end here, and 
that fibres concerned in vision leave by the anterior brachium. 
The internal geniculate body is an oval prominence 
situated on the antero-lateral part of the mid-brain in close re- 
lation with the optic thalamus. It receives the posterior bra- 
chium and sends out fibres to the optic tract, as stated, but 
has nothing to do with sight. 
THALAHENCEPHALON. 
The thalamencephalon includes optic thalamus, third ven- 
tricle, posterior perforated lamina, corpora albicantia, tuber 
cinereum, infundibulum, pituitary body, lamina cinerea, 
middle and posterior commissures, pineal gland, optic tracts, 
external geniculate body. 
This part of the brain is deeply placed and covered in at 
every point except a small area inferiorly, the interpeduncular 
space. It is a true part of the primary tube, but the fore 
brain, confined to a limited cavity in its extreme develop- 
ment, has folded back on top of this portion of the tube, "in 
fact slid all over it." Another example is given here of 
thickenings and thinnings of the original tube, the walls be- 
coming greatly thickened to form the optic thalami, while 
the floor is quite thin and the roof, reduced to a single layer 
of cells, adheres to the velum interpositum. 
The Optic Thalami are large oblong masses of grey mat- 
ter situated between the caudate nuclei of the corpora striata 
and resting on the crusta. Its dorsal surface presents a 
groove, better marked behind, which runs from the anterior 
part of the internal border obliquely backward and outward. 
The groove corresponds to the thickened margin of the fornix 
and divides the dorsal surface into an outer one-fourth and 
an inner three-fourths. The fourth external to the groove 
enters into the floor of the lateral ventricle and is limited 36 
externally by a band of white fibres the taenia semicircu- 
laris. It is broader in front where it presents a prominence, 
the anterior tubercle. The internal three-fourths of the 
dorsal surface is limited internally by the sharp edge separat- 
ing the dorsal from the mesial surface. It is broader behind 
and projects into neither of the ventricles. It has resting up- 
on it for the whole extent the velum interpositum. The 
posterior extremity of the thalamus is a rounded promi- 
nence known as the pulvinar, which projects over and par- 
tially conceals the brachia of the corpora quadrigemina. It lies 
partly in the descending horn of the lateral ventricle and is en- 
tirely external to the third ventricle. Below and external to 
the pulvinar is the outer geniculate body, placed just above 
the internal geniculate body (belonging to mid-brain) and 
separated from the latter by the anterior brachium. Inferi- 
orly the optic thalamus rests mainly on the tegmentum. The 
posterior portion, including the pulvinar and external genicu- 
late body, is free, while the anterior portion rests upon the 
white matter of the frontal lobe. The corpora albicantia and 
lateral parts of the tuber cinereum also bear an inferior rela- 
tion to the thalamus. Externally the optic thalamus is 
closely united to the internal capsule by a free interchange 
of fibres. The internal surface is plane and forms the 
lateral wall of the third ventricle. The main structure is 
of white and grey matter. The main elements of white 
matter are (1) the tegmentum, entering posteriorly, (2) an 
anterior tract to the frontal lobe, (3) a lower tract to the 
hemispheres, and (4) a tract to the lenticular nucleus. The 
grey matter is divided into a large lateral nucleus extend- 
ing into the pulvinar, a mesial nucleus, and an anterior 
nucleus located within the anterior tubercle. The nuclei 
are divided oft by white laminae. 
The Third. Ventricle is the portion of the central canal 
belonging to the thalamencephalon. It is a perpendicular 
slit-like expansion of the aqueduct of Sylvius between the 37 
optic thalami, deeper in front than behind and presenting 
two conical depressions in its floor. One of these lies over 
the optic commissure in the angle of the lamina cinerea, the 
optic recess; the other lies just behind it over the pituitary 
body, the infundibulum. At its posterior extremity be- 
neath the posterior commissure is the entrance of the aqueduct 
of Sylvius, while anteriorly we And a communication with 
each lateral ventricle by the foramen of Monroe,-a small 
opening between the anterior pillar of the fornix and the 
anterior extremity of optic thalamus. The boundaries of 
the ventricle are: Roof,-the under surface of velum inter- 
positum and choroid plexus, covered by a single layer of 
epithelium, and the posterior commissure. Laterally are 
the inner surfaces of the optic thalamus, which are almost 
in contact in the median line. Each surface is marked an- 
teriorly by a white curved band, convex forward, representing 
the buried anterior pillars of the fornix. On the Floor, in 
order from behind forward are the posterior perforated lamina, 
tegmentum, tuber cinereum, infundibulum, pituitary body, 
and lamina cinerea covering the optic commissure. The cor- 
pora albicantia do not enter into the floor. Anteriorly we 
have the main limb of the lamina cinerea, the anterior pillars 
of the fornix, and a single layer of epithelium covering the 
anterior commissure. Posteriorly the aqueduct of Sylvius. 
The posterior perforated lamina is the triangular 
lamina of grey matter, in reality a continuation of substantia 
nigra, bridging over the area between the diverging crusta. 
It extends as far forward as the corpora albicantia, where 
it becomes continuous with the tuber cinereum. The numer- 
ous perforations transmit small vessels. 
The tuber cinereum is a lamina of grey matter forming 
a part of the floor of the third ventricle. It is continuous 
with the posterior perforated lamina behind, opposite the cor- 
pora albicantia, and with the lamina cinerea in front, opposite 
the optic commissure. It extends beneath the optic thalamus 38 
on either side and in the middle is prolonged downwards and 
forwards as the conical infundibulum, to which is attached 
the pituitary body. 
The pituitary body is a small, reddish-grey, ovoid mass 
with its long axis in a transverse direction, which lies in the 
sella Turcica of the sphenoid bone. The body is surrounded, 
except at the pedicle, by dura mater. It consists of two lobes 
entirely different in appearance and origin. The anterior is 
much the larger, darker in color, developed from the buccal 
cavity, and has the structure of a secreting gland with alveoli 
and columnar epithelium. The posterior is embraced by the 
anterior and is a true outgrowth of the brain, in which the 
nervous structure is poorly developed and obscured by the in- 
growth of connective tissue. 
The corpora albicantia are two rounded bodies appear- 
ing wTell back in the interpeduncular space beneath the optic 
thalami. They each contain a grey nucleus which receives 
the fibres of the anterior pillar of the fornix, and send out a 
distinct bundle, that of Vicq d'Azyr, which ascends to the 
anterior nucleus of the optic thalamus. 
The lamina cinerea is a thin, L-shaped lamina of grey 
matter extending from the anterior termination of the corpus 
callosum in front to the optic chiasma behind, where it be- 
comes continuous with the tuber cinereum. The long arm 
is perpendicular and forms the anterior wall of the third ven- 
tricle, while the short arm is horizontal and lies directly on 
top of the chiasma. The angle so made forms the anterior 
or optic recess on the floor of the third ventricle. On either 
side the lamina is continuous with the grey matter of the 
anterior perforated laminae. 
The anterior perforated lamina is an outcropping of the 
slight connecting band of grey matter between the two parts 
of the corpus striatum. It is a triangular area, bounded pos- 
teriorly by the optic tract, internally and externally by the 
diverging roots of the olfactory nerve. The apex externally 39 
corresponds to the beginning of the fissure of Sylvius, while 
it is continuous at the base internally with the lamina cinerea. 
It is crossed by the peduncle of the corpus collosum, an 
indistinct, white band. The perforating vessels supply the 
corpus striatum. 
Optic tracts and commissure. The optic tracts curve 
around the crusta on either side, come together just in front 
of the tuber cinereum, decussate and pass on as optic nerves 
to the eye. The optic tract has two roots. The outer has 
an apparent and real origin in the external geniculate body. 
The inner is made up of fibres from the optic thalamus which 
emerge from the sulcus in front of the internal geniculate 
body ; and of the fibres of the anterior brachium, which pass 
between the two geniculate bodies as a twisted band to join 
the others. The fibres of the posterior brachium are only 
commissural, and are not concerned in sight. Only a part of 
the fibres of each optic tract decussate, the arrangement being 
such that each tract supplies the corresponding half of each 
eye. 
The Commissures. The anterior commissure is a 
rounded cord of white fibres placed transversely in front of 
the anterior pillars of the fornix, the epithelial wall of the 
third ventricle and the lamina cinerea. Laterally, the ends 
pass through the lenticular nucleus to the substance of the 
hemisphere. 
The middle commissure is a connecting band of grey 
matter between the middle nuclei of the optic thalami. It is 
a free cord, frequently broken, and placed a little in advance 
of the middle of the ventricle where the walls come nearest 
together. The posterior commissure is a flattened band 
of white fibres which overlies the entrance of the aqueduct 
of Sylvius into the third ventricle. Its fibres in part connect 
the optic thalami, in part are made up of the fibres of the 
posterior longitudinal bundle and of fibres from the nuclei 
of the III nerves. It is placed in front of the pineal gland 40 
and furnishes a lamina which contributes to the stalk of this 
body. The prolongation of the ventricle between this and 
the lamina formed by the union of the peduncles of the 
gland, is known as the pineal recess. 
The pineal gland, is a conical body resting in the groove 
between the upper corpora. It is attached by a broad stalk 
which is formed by the union of the lamina of the posterior 
commissure with the lamina formed by the convergence of 
the two peduncles of the pineal gland. The peduncles of the 
gland are two bands of white fibres which pass forward along 
the optic thalami, in the upper angles of the ventricle, and 
join the pillars of the fornix about the region of the foramen 
of Monroe. Traced backwards, the peduncles converge and 
at the same time expand into a lamina. The triangular 
area included between the peduncle, pulvinar and upper 
corpus, is known as trigonum habenulae (triangle of the 
bridle). The pineal gland is composed of a number of hol- 
low follicles, containing gritty, calcareous matter, and separa- 
ted by ingrowths of connective tissue. It is a true outgrowth 
of the brain. In some animals the stalk is much elongated 
and passes to the surface of the skull, in which case the gland 
has been supposed to be an eye, capable of receiving impres- 
sions, and the stalk an optic nerve. 41 
PROSENCEPHALON. 
Under the prosencephalon we include the lateral ven- 
tricle, corpus callosum, fornix, septum lucidum, corpora 
striata, taenia semicircularis, velum interpositum, internal 
capsule, etc. 
The lateral ventricle is the central canal of this part 
of the brain, much distorted by the complex development. 
It may be described as consisting of a body, anterior, pos- 
terior and descending horn. The body extends from the 
foramen of Monroe to the extremity of the pulvinar. In the 
normal condition the ventricle would appear as a transverse 
slit with its roof and floor in contact. The anterior cornu 
runs forward, downward and outward from the foramen of 
Monroe into the frontal lobe. It is separated from its fellow 
of the opposite side by the septum lucidum alone. The 
posterior cornu passes backward, in a curve which is con- 
vex outward, into the occipital lobe. The descending horn 
is the part of the ventricle taken along with the temporo- 
sphenoidal bud in development, but it is not in the center of 
its mass, because, internally, we find only a single layer of 
the epithelium, while the whole mass of the lobe lies external 
to it. The boundaries of each part of the ventricle are best 
expressed in tabulated form : 42 
ROOF. 
ANT. WALL. 
INNER WALL. 
FLOOR. 
OUTER WALL. 
Anterior 
Cornu. 
Corpus 
Callosum. 
Genu of Cor- 
pus Callo- 
sum. 
Septum 
Lueidum. 
1. The angle of 
junction of 
caudate n. 
and Se p- 
turn Luci- 
dum. 
2. Rostrum of 
Corpus Cal- 
losum. 
Caudate 
nucleus. 
Body. 
Corpus 
Callosum. 
(tapetum) 
1. Septum 
Lueidum, 
2. Junction of 
fornix 
and Corp. 
Call. 
1. Caudate u. 
2. TaeniaSem- 
icircularis. 
3. Optic Thal- 
amus. 
4. Choroid 
plexus. 
5. Fornix- 
(a) body. 
(&) post.pillar. 
No outer wall. 
An angle of 
junction be- 
tween Corp. 
Call, and 
white mat- 
ter. 
Descend!'g 
Cornu. 
(1) Corp. Call. 
(2) Pulvinar. 
(3) Int. Cap- 
sule. 
(4) Taenia 
Semicir- 
cularis. 
(5) Surcingle. 
Transverse 
fissure. 
(1) 
collateralis. 
(2) Hippocam- 
pus major. 
(3) Pes hippo- 
campi. 
(4) Corpus 
Fimbria- 
turn. 
(5) Choroid 
plexus. 
White matter 
of Temporo- 
Sphenoidal 
lobe. 
Posterior 
Cornu. 
Corpus 
Callosum. 
Bulb caused 
by forceps 
major. 
Hippocam- 
pus minor. 
White matter 
of occipital 
lobe. 
The optic thalamus does not in reality form a part of 
the floor of the body of the lateral ventricle. The floor of 
the ventricle, between the edge of the fornix and the taenia 
semicircularis, has become thinned to a single layer of cells, 
but this layer is, nevertheless, still the true floor. The optic 
thalamus merely happens to lie under this part, and, 
practically, when we see the floor of the ventricle we see the 
optic thalamus through the single layer of cells. In other 
words, the optic thalamus never formed a part of the prosen- 
cephalon, and therefore cannot form a wall to its cavity. 
The taenia semicircularis is a narrow band of white 
fibres, which lies in the groove separating the caudate nucleus 43 
from the optic thalamus. It takes its origin in the nucleus 
amygdala, at the apex of the desending horn of the ventricle, 
passes up in the roof of the cornu and curves around into 
the floor of the body of the ventricle. A part, at least, of 
its fibres join the anterior pillar of the fornix near the fora- 
men of Monroe; the rest are uncertain. 
The corpus callosum, or great commissure, is the con- 
necting band between the two cerebral hemispheres seen at 
the bottom of the great longitudinal fissure. It connects the 
hemispheres throughout nearly half their length, approaches 
closer to the front than the back, and has a thickness con- 
siderable in all parts but greatest at the ends. The upper 
surface is principally marked by transverse striae, but presents 
on either side of the median line longitudinal white bundles, 
the nerves of Lancisi. On each side, near the margin, are 
seen other longitudinal striae. Both sets are traced posteri- 
orly into the gyrus dentatus (fascia dentata). In front the 
corpus callosum is reflected downward and backward, form- 
ing a bend named the genu. The reflected portion, termed 
the rostrum, becomes gradually narrower as it descends and 
is connected with the lamina cinerea by a thin white layer. 
It gives off also two bands of substance, the peduncles of 
the corpus callosum, which diverge from one another, run 
across the anterior perforated space to the tip of the tem- 
poral lobe. Traced upwards around the genu these pedun- 
cles are found to be continuous with the nerves of Lancisi. 
Behind, the corpus callosum terminates in a free thickened 
border named the splenium. The mesial part of the under 
surface of corpus callosum is connected with the fornix be- 
hind and in the rest of its length with the septum lucidum. 
On the sides it forms the roof of the anterior horn and body 
of the lateral ventricle. The fibres pass in a radiating man- 
ner, interlacing with those of the internal capsule, through 
the medullary substance to the cortex. Those fibres which 
sweep round into the prefrontal region form the forceps 44 
minor, those curving over the lateral ventricle take the 
name of tapetum, while the large mass of fibres of the 
splenium curves round into the occipital lobe as the forceps 
major, making the prominence of the bulb in the posterior 
cornu just above hippocampus minor. 
The Septum Lucidum is a double partition between 
the lateral ventricles, which occupies the interval between 
the corpus callosum above and in front, and the fornix below 
and behind. It tapers behind to end over the middle of the 
third ventricle, and below to end at the anterior commissure. 
The two laminae are distinct and have the interval of the 
fifth ventricle between them. The fifth ventricle was 
originally a part of the great longitudinal fissure. Below 
where the pillars of the fornix descend the two laminae are 
separated slightly. 
The Fornix is an arched longitudinal white tract con- 
sisting of two lateral halves which are separated from one 
another in front and behind but joined together in the mid- 
dle. The body or middle conjoined part is broad and flat- 
tened behind where the corpus callosum rests on it, narrower 
in front where it is attached to the septum lucidum. Its 
lateral edges appear in the lateral ventricles. Ventrally it is 
separated from the optic thalamus and third ventricle by the 
velum interpositum. The anterior pillars are two rounded 
cords, slightly separated, which pass down in front of the 
foramen of Monroe and through the grey matter of the 
walls of the third ventricle to the corpora albicantia 
where they end. Each pillar is connected near the foramen 
of Monroe with the fibres of the peduncles of the pineal 
gland and a part of the fibres of the taenia semicircularis. 
The posterior pillars are the two flat posterior prolonga- 
tions, which diverge rapidly and pass down over the pulvinar 
into the descending horns of the lateral ventricles. Here 
some of the fibres are distributed to the surface of the hip- 
pocampus major, and the remainder are continued into the 45 
corpus fimbriatum. On lifting up the conjoined posterior 
pillars and corpus callosum a triangular area is seen be- 
tween the two pillars marked by transverse, oblique and 
longitudinal fibres to which the term lyra has been given. 
The foramen of Monroe is the communicating aper- 
ture between the third and lateral ventricles. It is placed 
between the anterior end of the optic thalamus and the an- 
terior pillar of the fornix, and is bounded superiorly by the 
body of the fornix. 
The corpora striata are two large ovoid masses of grey 
matter situated in front and to the outer side of the optic 
thalami. The greater part of each is situated in the white 
substance of the hemispheres and known as the lenticular 
nucleus, while a smaller part appears in the lateral ventricle 
as the caudate nucleus. 
The caudate nucleus is pyriform in shape with its 
large end projecting anteriorly into the frontal lobe and 
forming the external wall of the anterior horn and a part of 
the floor of the body of the lateral ventricle. The tail or 
surcingle is the tapering portion that passes backward and 
outward in the floor of the body of the ventricle, curves 
into the roof of the descending horn and extends almost to its 
extremity. The caudate nucleus is separated from the optic 
thalamus by the taenia semicircularis; from the lenticular 
nucleus by the anterior limb of the internal capsule. The 
lenticular nucleus is only seen on section of the hemi- 
sphere. It is separated from the caudate nucleus by the in- 
ternal capsule, except for a small band at the anterior inferior 
extremity; from the claustrum externally by the external 
capsule. On longitudinal section it is lense-shaped and is 
seen to have an antero-posterior diameter corresponding 
closely to that of the island of Reil. On transverse vertical 
section it is of triangular shape and divided by white laminae 
into an outer striated zone, the putamen, and two inner 
zones known conjointly as the globus pallidus. 46 
The internal capsule is a lamellated tract of white 
fibres, the direct continuation upward of the crusta, which 
lies between the optic thalamus, caudate nucleus and taenia 
semicircularis mesially and the lenticular nucleus laterally. 
Above, it radiates as the corona radiata to the cerebral cor- 
tex. Roughly the middle third passes to the Rolandic 
region, the anterior third to the frontal, and the posterior 
third to the occipital region. In horizontal section the 
internal capsule has a bend, the genu, opposite the taenia 
semicircularis, of 120°. In vertical section it appears as a 
straight band running upward and outward. Besides the 
fibres of the crusta it receives others from the caudate and 
lenticular nuclei, the optic thalamus and corpus callosum. 
The external capsule is a thin, white lamina bounding 
the lenticular nucleus externally and separating it from the 
claustrum. 
The claustrum is a thin isolated grey lamina, which 
corresponds in length to the island of Reil. The surface 
next to the external capsule is smooth but the outer surface 
is irregularly ridged. 
The velum interpositum or tela choroidea superior 
is a vascular membrane formed of two layers of pia mater 
pushed into the interior of the brain through the great 
transverse fissure. It is triangular in shape, overlies the 
third ventricle and inner three-fourths of the optic thalamus, 
and is placed directly under the body of the fornix. Its 
apex is bifid at the foramen of Monroe, its sides project 
into the lateral ventricles as the choroid plexus from under- 
neath the fornix, and the base is continuous with the gen- 
eral pia mater. Large veins, the Vanae Geleni, run between 
its layers. 
The hippocampus minor is the prominence in the 
floor of the posterior cornu of the lateral ventricle caused 
by the pushing inward of the brain substance by the calcarine 
fissure on the mesial surface of the hemisphere. 47 
The hippocampus major which occupies the whole 
length of the floor of the descending cornu, is in a like man- 
ner formed by the hippocampal or dentate fissure. This 
and the eminentia collaterals are best understood by refer- 
ence to the diagrams. The lower end of the hippocampus 
major is enlarged, has notched edges and is known as the 
pes hippocampi. 
The eminentia collateralis is a rounded prominence 
situated in the angle of divergence of the hippocampus 
major and minor and running down into the descending 
cornu parallel to the hippocampus major. It is caused by 
collateral fissure protruding inward. 
The corpus fimbriatum is the prolongation downward 
of the posterior pillar of the fornix which passes along the 
concave edge of the hippocampus major to end in the white 
matter of the uncus. It represents the white matter of the 
hemisphere which here comes to the surface along the edge 
of the dentate gyrus. It exists only in the descending horn. 
The fascia dentata is the name given to the peculiarly 
toothed and notched free edge of the dentate gyrus, where 
its grey matter stops short at the surface just below the great 
transverse fissure. It does not enter into the lateral ventricle 
as the figure will show. It begins posteriorly just above and 
behind the splenium in the nerves of Lancisi, passes down 
along the upper border of the hippocampal gyrus to the 
uncus where it becomes lost. 
The great transverse fissure is a line of a horseshoe 
shape along which is found only a single layer of epithelium 
between the lateral ventricle and the external surface of the 
brain. Beginning forward beneath the lateral edge of the 
body of the fornix it follows the plane of the body and pos- 
terior pillar of the fornix down into the descending cornu of 
the ventricle to its apex. The fissure, then, would lie be- 
tween the body of the fornix and the optic thalamus, above: 
between the posterior pillar of the fornix and the pulvinar a 48 
little further back; between the under surface of the pulvinar 
and the corpus fimbriatum in the first part of the descending 
cornu; and finally between the white matter of the cerebrum 
and the corpus fimbriatum nearer the apex. Throughout 
the whole length of the fissure the pia mater pushes into the 
ventricle to form the many convolutions of the choroid 
plexus, and pushes ahead of it a single layer of cells. This 
single layer of cells represents the primary wall of the ven- 
tricular canal thinned down to this degree in the course of 
development. Throughout the whole course the layer of 
cells extends, as abridge of tissue following every convolution 
of the choroid plexus, between the edge of the fornix on the 
one side and the taenia semicircularis on the other. If the 
pia mater is pulled away from this region the single layer of 
cells is torn away and the lateral ventricle is open for the 
whole length of the great transverse fissure. 
Cerebral Lobes and Convolutions. 
That each cerebral hemisphere possesses an outer con- 
vex, an inner plane, an inferior irregular surface, and an 
anterior and posterior more or less pointed extremity is 
easily enough understood. This whole area is made up of 
gyri, marked off by sulci, each of varying extent and dimen- 
sions. 
Certain of the major sulci are arbitrarily taken to 
divide up the entire surface into definite areas or lobes each 
with a varying number of convolutions. 
Thus the Frontal lobe occupies the area in front of 
the fissure of Rolando, and above the vertical limb of the 
fissure of Sylvius. Its ascending frontal (or precentral) 
gyrus runs parallel to the fissure of Rolando. The remain- 
ing area of the lobe is occupied by three longitudinal gyri, 
which run on around anteriorly to form the three orbital 49 
gyri on the inferior or orbital surface of the lobe. The first 
gyrus appears on the mesial surface as the marginal gyrus, 
separated from the limbic lobe by the calloso-marginal fissure. 
The posterior part of this gyrus is nearly cut off from the 
rest by an ascending sulcus, and is called the paracentral 
lobule. 
The Parietal lobe is limited, in front by the fissure of 
Rolando, behind by the parieto-occipital and anterior occi- 
pital sulcus, below by the horizontal limb of Sylvius, and 
on the mesial surface by calloso-marginal, parieto-occipital 
and post-limbic sulci. Its gyri are: ascending parietal 
(parallel to Rolando), superior parietal, supramarginal 
(curving over end of Sylvius), angular (curving over end 
of parallel fissure), post parietal, and precuneus or 
quadrate lobe, as indicated in diagram. 
The Temporal lobe includes the lower prominent area, 
limited above by the horizontal limb of the fissure of 
Sylvius, behind by the anterior occipital sulcus, and 
mesially by the calcarine sulcus. Its gyri are the first, 
second, third, fourth and fifth (or lingual) temporal 
gyri, separated by corresponding sulci. 
The Occipital lobe includes the remaining limited area 
behind the parieto-occipital and anterior occipital sulcus, and 
the cuneus on the mesial surface which is included between 
the parieto-occipital and calcarine sulci. The gyri are too 
small and inconstant for description. 
The Central lobe, or Island of Reil is a triangular 
area of gyri and sulci at the beginning of the fissure of 
Sylvius, which is continuous with the general surface, but 
has been covered in by the overhanging operculum and sur- 
rounding gyri. It corresponds in position and extent to the 
corpus striatum. The Island is separated from the adjacent 
parts by the sulcus limitans insulae which almost 
entirely surrounds it. 50 
The Limbic lobe (a morphological lobe) is a long, 
rather narrow area, making almost a complete oval on the 
mesial surface of the hemisphere. It is arranged, as indica- 
ted by the dotted area in the diagram, about the corpus 
callosum and descending horn of the lateral ventricle. It 
includes gyrus fornicatus, dentate gyrus (or fascia), 
corpus fimbriatum, hippocampal gyrus and sulcus. 
The Olfactory lobe is rudimentary in man and is rep- 
resented by the olfactory bulb, an oval body about one 
c. m. long, placed in the first frontal sulcus on the orbital 
surface of the frontal lobe. This body gives off posteriorly 
a band of white matter, the olfactory tract which divides 
into an outer and inner root. The outer root passes across 
the anterior perforated space to the tip of the temporal lobe, 
and ends in the anterior part of the hippocampal gyrus, or 
according to Luys in the nucleus amygdala. The inner 
root recurves sharply and enters the anterior end of the 
limbic lobe. It will thus be seen that the olfactory bulb, 
tract, and roots connect the two ends of the limbic lobe and 
roughly complete a racket shaped figure. INDEX.-Of Brain. 
Acoustic fibres12,17 
" tubercle 18 
Ala 26 
" cinerea 18 
Amygdala 27 
Ant. Commissure 39 
" pillars of fornix 44 
" pyramidal tract. 12 
" tubercle 36 
Aqueduct of Sylvius 31 
Arbor vitae 28 
Arcuate fibres 12,21 
" " ext 21 
" "int20,21 
Band, furrowed 27 
Body of fornix 44 
Brachia of Corp. Quad 34 
Bundle, post-longitudinal.. . . 24, 32 
Burdach, tract of 14 
Calamus Scriptorius 15 
Calcarine Fissure 46 
Capsule ext 46 
" int43, 46 
Caudate nucleus 20,45 
Cerebellar tract 13 
Cerebellum 24 
Cerebral hemispheres 41 
Chiasma 39 
Choroid plexuses17, 46, 48 
Claustrum45, 46 
Clava 14 
Collateral eminence 14 
Commissures ant 39 
" middle 39 
" post 39 
of Gudden 34 
" optic 39 
Convolutions 48 
Cornucopia 17 
Corona radiata 46 
Corpora albicantia39, 44 
" geniculata35,36 
" quadrigemina 34 
" striata 45 
Corpus callosum 43 
" fimbriatum 47 
" trapezoides 28 
Course of fibres 23 
Crescentric lobes 26 
Crossed pyramidal tract 12 
Crura cerebri 31 
Crusta 30, 31 
PAGE 
Culmen 26 
Cuneate funiculus 14 
Curved sensory tract 32 
Cuneus 48 
Declive 26 
Decussation of fillet 20 
" pyramids 12 
Dentate nucleus 28 
" fissure 47 
Digastric Lobe 28 
Direct cerebellar tract 13 
" pyramidal " 12 
Eminentia cinerea 18 
" collateralis 47 
External capsule 45 
" geniculate body.... . 36 
Fascia dentata 47 
Fibres traced 23 
Fillet14, 20, 22, 33 
" lower 33 
" upper 33 
" middle 33 
Fissures 48 
Flocculus17, 27 
Folium cacuminus 26 
Foramen Caecum 11 
" of Monroe37, 45 
" of Majendie 16 
Forceps major 44 
" minor 44 
Formatio reticularis 19 
Fornix 44 
Fovea inf 17 
" sup 18 
Fraenulum15, 25 
Funiculus cuneatus 14 
" teres 17 
" gracilis. 14 
" of Rolando 13 
Furrowed band 27 
Galeni veins 46 
Geniculate body, ext 36 
" " int 35 
Genu corp. call.... 43 
" int. capsule 46 
Globus pallidis 45 
Goll, tract of.. 14 
Great transverse fissure 47 
" horizontal " '. 25 
Hippocampus major 46 
" minor 47 
Hippocampal fissure 47 
PAGE INDEX. 
Infundibulum 37, 38 
Lamina, ant. perf . 38 
" post, perf 34,37 
" cinerea 39 
Lancisi. 43 
Lateral tract 12 
" ventricle 41,42 
" recess 15 
" angle 15 
" sulcus 30 
Lenticular nucleus 45 
Ligula 17 
Lingula 15, 25 
Lobulus centralis 26 
Lobus coeruleus 18 
Lyra 45 
Majendie .... 16 
Medulla 11 
Medullary velum, inf 16 
" " sup 15 
Monroe, foramen of 37-45 
Nodule 16, 27 
Nucleus of aqueduct 31 
" auditory 18 
" caudatus 20,45 
" dentatus 28 
" lenticular 45 
" olivary 13,20 
" " sup 22 
" red 29,33 
" gracilis 20 
" cuneatus 20 
Obex 17 
Olfactory roots 38 
Olivary body 13,20 
Optic chiasma 39 
" commissure 39 
" recess 36,38 
" thalamus 35,42 
" tract 39 
Peduncles of cerebellum 22, 28 
" corp, call 43 
" olivary 21 
cerebrum 30 
pineal gland 40 
Perforated lamina, ant 38 
" " post 34,37 
Pes hippocampi 47 
Pillars of fornix 44 
Pineal gland 40 
" recess 40 
Pituitary body 39 
Pons 22 
Post.-longitudinal bundle 24, 32 
Post.-sup. lobe cerebellum 26 
Prosencephalon 41 
Pulvinar 36 
Putamen 45 
Pyramid of worm 27 
" " medulla 12 
" decussation of 12 
Quadrate lobe 26 
Quadrigeminal bodies 34 
Raphe of Pons 22 
" medulla 20 
Recess, lateral 15 
" optic 36,38 
" pineal 40 
Red nucleus : 29, 33 
Restiform body 13, 30 
Rolando, fissure of 48 
" tubercle of 14 
" funiculus of 13 
Rostrum 43 
Semilunar lobe 28 
Septuni lucidum 43,44 
Slender lobe 28 
Splenium 43 
Substantia nigra 30, 33 
" ferruginea 18 
Subthalmic region 32 
Superficial arched fibres.... 21 
Taenia semicircularis......... 36, 43 
Tapetum 44 
Tegmentum 30, 32 
Tela choroidea, inf 16 
" " sup 46 
Tent 16 
Thalamencephalon 35 
Thalamus, optic 35,42 
Third ventricle 36 
Tonsil . . 27 
Trapezium 23 
Trigonum habenulae 40 
" hypoglossi 18 
Tuber cinereum 37 
" valvulae 28 
Tubercle of Rolando 14 
" cuneate 14 
Uncus 47 
Uvula 27 
Valecula 24 
Valve of Vieussens 15,25 
Velum interpositum 36,46 
" sup. medullary 15 
" inf " 16 
Ventricle, fourth 14,18 
" lateral 41,42 
" third 36 
" fifth 44 
Vicq d' Azyr 39 
White lamina 33 
Worm 24