§8 
1 lie meninges, or membranes of the. brain, 
ere two in number ; one of which is very 
strong, and lies contiguous to the cranium; 
the other is very thin, and immediately 
touches the brain. The first is named dura 
mater, the second pia mater. The last is 
again divided into two, the external lamina 
being termed arachnoides, the internal re- 
taining the common name of pia mater. From 
the former are the falx pentorium, & c. which 
are septa of the brain, while the latter more 
immediately invest the cerebral mass. 
Cerebrum. 
Situation and figure,— The cerebrum, pro- 
perly so called, is a kind ot medullary mass, 
of a moderate consistence, and of a greyish 
colour on the outer surface, filling all' the 
superior portion of the cavity of the cranium; 
or that portion which lies above the trans- 
verse septum. The upper part of the cere- 
brum is of an oval figure. It is flatter on the 
lower part, each lateral half of which is di- 
vided into three eminences, which correspond 
with the cavities at the base of the cranium. 
Division and lobes. — The cerebrum is di- 
vided into two lateral portions, separated by 
the falx, or great longitudinal septum of the 
dura mater. They are generally termed 
hemispheres, but they are more like quarters 
of an oblong spheroid. Each of these por- 
tions is divided into two extremities, one an- 
terior, and one posterior, which are termed 
the lobes of the cerebrum, between which 
there is a large inferior protuberance, which 
goes by the same name; so that in each he- 
misphere there are three lobes, one anterior, 
ine middle, and one posterior. The anterior 
and middle lobes of the cerebrum on each side 
are parted by a deep p arrow sulcus, termed 
tissura magna sylvii. 
Sides and inequalities. — Each lateral por- 
tion of the cerebrum has three sides; one su- 
perior, which is convex, one inferior, which 
is uneven, and one lateral, which is Hat, and 
turned to the falx. Through the whole sur- 
face ot these three sides, we see inequalities, 
er windings, like the circumvolutions of intes- 
tines, formed like weaving streaks or furrows, 
very deep and narrow, into which the septa, 
©r duplicatures of the pia mater, insinuate 
themselves, and thereby separate these cir- 
cumvolutions from each other. 
Near the surface of the cerebrum, these 
circumvolutions are at some distance from 
each other, representing serpentine ridges; 
and in the interstices between them, the su- 
perficial veins of the cerebrum are lodged. 
Substance. — r J lie substance of the cerebrum 
is of two kinds, distinguished by two different 
colours, one part of it being of a greyish or 
ash colour, the other, which is somewhat 
firmer than the former, is remarkably white, 
but redder in the foetus. The ash-coloured 
substance lies chiefly on the outer part of the 
cerebrum, like a kind of cortex, whence it has 
been named substantia corticalis, or cinerea. 
'I he white substance occupies the inner part, 
and is termed substantia medullaris, or sub- 
stantia alia. T his abounds in greater quan- 
tity than the other, and in many places is per- 
forated with red arteries. 
Corpus callosum. — Having cut off the falx 
from the crista galli, and turned it backward; 
it we separate gently the two lateral parts or 
hemispheres ot the cerebrum, we see a lon- 
gitudinal portion of a white convex body, 
ANATOMY. 
which is named corpus callosum, Both ex- 
tremities of this medullary body terminate 
by a small edge, bent transversely downward. 
Medullary arch and centrum ovale.— The 
corpus callosum becomes afterward conti- 
nuous on each side, with the medullary sub- 
stance, which, through all the remaining parts 
of its extent, is entirely united with the cor- 
tical substances and together with the cor- 
pus callosum forms a medullary arch or vault, 
of an oblong or oval figure. To perceive 
this, the whole cortical substance, together 
with the medullary laminae mixed with it, 
must be cautiously and dextrously cut in the 
same direction with the convexity of the ce- 
rebrum. 
Ventriculi laterales. — Under this arch are 
two lateral cavities, much longer than thev 
are broad, and very shallow, separated by a 
transparent medullary septum ; of which here- 
after. These cavities are generally named 
the lateral ventricles of the brain. 
The lateral ventricles are broad, and 
rounded at those extremities which lie next 
the transparent septum. They go from be- 
fore backward, contracting in breadth, and 
separating from each other gradually in their 
progress. Afterward they bend downward, 
and return obliquely from behind forward, 
in a course like the turning of a ram’s horn, 
and terminate almost under their superior ex- 
tremities, only a little more backward and 
outward. 
At the posterior part, where they begin to 
bend downward, there is on each side a par- 
ticular elongation, which runs backward, and 
terminates in a triangular pointed cavity, 
turned a little inward, the two points resemb- 
ling horns. These ventricles are every where 
lined with a continuation of the pia mater. 
Septum lucidum. — The transparent parti- 
tion, or septum iucidum, as it is commonly 
called, lies directly under the raphe, or su- 
ture of the corpus callosum, of which it is a 
continuation, and a kind of duplicature. It 
is made up of two medullary lamina?, more 
or less separated from each other bv a nar- 
row medullary cavity, sometimes filled with a 
serous substance. 
Fornix. — The septum lucidum is united by 
its lower part, to the anterior portion of the 
particular medullary body, called improperly 
the fornix with three pillars. It is in reality 
nothing but the corpus callosum ; the lower 
side of which is like a hollow ceiling, with 
three angles, one anterior, and two posterior, 
and three edges, two lateral and one poste- 
rior. The lateral edges are terminated each 
by a large semicylindrical border, like two 
arches, which, uniting at the anterior angle, 
form by their union what is called the anterior 
pillar of the fornix; and as they run backward 
separately toward the two posterior angles, 
they have then the name of the posterior pil- 
lars. 
The anterior pillar being double, is larger 
than either of the posterior ; and the marks of 
this - duplicity always remain. Immediately 
below the basis of this pillar we observe a 
large, white, short medullary rope, stretched 
transversely between the two hemispheres, 
and commonly called the anterior commissure 
of the cerebrum. It is to this pillar that the 
septum lucidum adheres. The posterior pil- 
lars are bent downward, and continue through 
the lower portions of the ventricles all the way 
to their cavities, resembling a ram’s horn. 
which is ci name that has been given to them. 
They diminish gradually in thickness during 1 
this course, and at their outsides have each a 
small, thin, Hat, collateral border, to which ] 
the name of campora fimbriata is applied. 
'I he posterior pillars of theemra ot the fornix 
unite with two medullary protuberances, call- 
ed pedes hippocampi, ’i lie inferior surface 
of the triangular ceiling, which lies between 
these arches, is full of transverse, prominent, ! 
medullary lines; for which reason the ancients I 
called it psallo.des and lyra, comparing it to a I 
stringed instrument, something like what is I 
now called a dulcimer. 
Under the fornix, and immediately behind 
its anterior crura, there is a hole, the'ibramen i 
Monroi, of a considerable size, by which the | 
two lateral ventricles communicate, and an- \ 
other passage leads down from this under the ] 
different appellations of foramen commune 1 
anterius, valva, iter ad infundibulum, but more I 
properly iter ad tertium ventriculum. 
Eminences. — 'I he fornix being cut off, ] 
and inverted, or quite removed, we see first ] 
of all avascular web, called plexus choroides, 
and several eminences move or less covered j 
by the expansion of that piexus. There are 1 
four pairs of eminences, which follow each I 
other very regularly, two large, and two J 
small. live first two great eminences are 1 
named corpora striata, and the second tha- | 
land nervorum opticorum. The four small J 
eminences are closely united together; the 1 
anterior being called nates, and the posterior I 
testes ; but it would be better to call them 1 
simply anterior and posterior tubercles. Im- 1 
mediately before these tubercles, there is a | 
single eminence, called glandula pinealis. 
Corpora striata. — -The corpora striata got 1 
that name, because, by cutting them with tire 1 
knife, we meet with a great number of white I 
and ash-coloured lines,' alternately disposed, I 
which arc only the transverse sect'on of the 1 
medullary and cortical laminae, mixed toge- 1 
ther, in a vertical position, in the basis of the 1 
cerebrum, as appears evidently by incisions 1 
made from above downward.* ’t hese two 1 
eminences are of a grej ish colour on the sur- 1 
face, oblong, roundish, pyriform, and larger 1 
on the fore than on the back part, where they J 
are narrow and bent. J 1 
They lie in the bottom of the superior ca- 1 
vity of the lateral ventricles, which they re- 1 
seinble in some measure in shape, their an- 1 
lerior parts being near the septum lucidum, 1 
from which they separate gradually, as they I 
run backward, and diminish in size. They 1 
are in reality the convex bottoms of the ven- 1 
tricles ; and it is at the lower part of the in- 1 
terstice, between the largest, portions of them, j 
that we observe the greatest transverse cord, j 
termed the anterior commissure of the cere- ] 
brum, which we mentioned already in de- .] 
scribing the anterior pillar of the fornix. 1 
I his cord communicates more particularly 1 
with the bottom of the corpora striata, bv a 1 
turn toward each side. 
Thalami nervorum opticorum. — The tha- 1 
ianvi nervorum opticorum are so named, be- J 
cause these nerves rise chiefly from them. 1 
They are two large eminences by the side of 1 
each other, between the posterior portions or I 
the extremities of the corpora striata. Their ] 
figure is semispheroidal, and a little oval, and | 
they are of a whitish colour on the surface, 1 
and their inner substance is partly greyish ] 
and partly white ; so (hut in cutting them we I 
