59 2 ANA 1 
are eafily feparable at the bafts, and through the whole 
length of the fpinal marrow. 
The cerebrum is a kind of medullary mafs, of a mode- 
rate confidence, and of a greyifli colour on the outer fur- 
face, filling all the fuperior portion of the cavity of the 
cranium, or that portion which lies above the tranfverfe 
feptum. The upper part of the cerebrum is of an oval 
figure, like half an egg cut iengthwife, or rather like two 
quarters of an egg cut Iengthwife, and parted a little from 
each other. It is flatter on the lower part, each lateral 
half of which is divided into three eminences, w hich cor- 
refpond with the cavities at the bafe of the cranium. The 
cerebrum is divided into two lateral portions, feparated 
by the falx, or great longitudinal feptum, of the dura ma¬ 
ter. They are generally termed hemispheres, but they are 
more like quarters of an oblong fpheroid. Each of thefe 
portions is divided into two extremities, one anterior and 
one pofterior, which are termed the lobes of the cerebrum, 
between w hich there is a large inferior protuberance which 
goes by the fame name; fo that in each hemifphere there 
are three lobes, one anterior, one middle, and one pofterior. 
The fubftance of the cerebrum is of f\vo kinds, diftin- 
guifhed by two different colours; one part of it being of 
a greyifli or afh colour; the other, which is fomewhat 
firmer than the former, is remarkably white, but redder 
in the foetus. The afh-coloured fubftance lies chiefly on 
the outer part of the cerebrum like a kind of cortex, from 
whence it has been named fubjlantia corticalis, or cincrca. 
The white fubftance occupies the inner part, and is named 
fubjlantia medullaris, or limply fubfantia alba. T his abounds 
in greater quantity than the other, and in many places is 
perforated with red arteries. If we feparate gently the 
two lateral parts or liemifpheres of the cerebrum, we fee 
a longitudinal portion of a white convex body, which is 
named corpus callofum. The Surface of it is covered by 
the pia mater, which runs in between the lateral portions 
of this body and the lower edge of each hemifphere. 
Along the middle of its furface, from one end to the other, 
a kind of raphe is formed, by a particular intertexture of 
fibres crofting each other. This raphe is made more per¬ 
ceivable by two fmall medullary cords, which accompany 
it on each fide, and adhere clofely to the tranfverfe fibres. 
The corpus callofum becomes afterwards continuous on 
each fide with the medullary fubftance; which, through 
all the remaining parts of its extent, is entirely united 
■with the cortical fubftance, and, together with the corpus 
callofum, forms a medullary arch or vault of an oblong 
.or- oval figure. Under this arch are two lateral cavities, 
feparated by a tranfparent medullary feptum. Thefe ca¬ 
vities are generally named the anterior fuperior ventricles of 
.ike cerebrum, to diftinguifh them from two other finaller 
cavities which are fituated more backward; but the name 
of lateral or great ventricles, given them by Steno, is more 
proper than either of the other two. The tranfparent par¬ 
tition, or feptum lucidum, as it is commonly called, lies di- 
redily under the raphe or future of the corpus callofum, 
of which it is a continuation and a kind of duplicature. 
It is united, by its lower part, to the anterior portion of that 
particular medullary body, improperly called the fornix, with 
three pillars, becaufe of fome refemblance it is thought to 
-bear to the arches of ancient vaults. It is, in reality, no¬ 
thing but the corpus callofum; the lower fide of which is 
like a hollow cieling with three angles, one anterior, and 
two pofterior ; and three edges, two lateral, and one pofte¬ 
rior. The lateral edges are each terminated by a large 
femicylindrical border, like two arches, which, unitingat 
the anterior angle, form by their union what is called the 
anterior pillar of the fornix ; and, as they run backward fe- 
parately toward the two pofterior angles, they have then 
the name of the poferior pillars. The anterior pillar be¬ 
ing double, is larger than either of the pofterior ; and the 
marks of this duplicity always remain. Immediately be¬ 
low the bafis of this pillar, we obferve a large, white, 
ftiort, medullary, rope, firetched tranfverfely between the 
1 O M Y. 
two liemifpheres, and- commonly called the anterior com - 
mijfure of the cerebrum. The pofterior pillars are bent 
downward ; and at their outfides they have each a fmall, 
thin, flat, collateral, border, to which the name of corpora 
fmbriata is applied. The pofterior pillars alfo unite with 
two medullary protuberances, called pedes hippocampi. The 
inferior furface of the triangular ceiling, which lies be¬ 
tween thefe arches, is full of tranfverfe prominent medul¬ 
lary lines; for which reafon the ancients called it pfalloides 
and lyra, comparing it to a ftringed inftrument, fomething 
like what is now called a dulcimer. Under the fornix, 
and immediately behind its anterior crura, there is a hole 
of confiderable fize, by which the two lateral ventricles 
communicate ; and another paffage leads down from this, 
under the different appellations of foramen commune anteri- 
us, vulva, iter ad infundibulum, but more properly iter ad 
tertium ventriculum. The fornix being cut eft' and invert¬ 
ed, we fee firll of all a vafcular web, called plexus cko- 
roiclcs, and feveral eminences more or lefs covered by the 
expanfion of that plexus. There are four pairs of emi¬ 
nences which follow each other very regularly, two large 
and two fmall. The firft two great eminences are named 
corpora f rial a ; and the fecond, thalami nervorum opticorum. 
The four fmall eminences are clofely united together, the 
anterior being called nates, and the pofterior tefles-, but it 
would be better to call them Amply anterior and poferior 
tubercles. Immediately before thefe tubercles there is a 
fingie eminence, called glandula pinealis. Immediately un¬ 
der the union or beginning of the thalami nervorum opti- 
corum, lies a particular-cavity called the third ventricle of 
the cerebrum. It opens backwards into the paflage called 
iter ad quartum ventriculum. Between the bafis of the an¬ 
terior pillar of the fornix, and the anterior part of the 
union of the optic thalmi, lies a fmall medullary canal, 
named infundibulum. It runs down towards the balls of 
the cerebrum, gradually contracting, and terminates by a 
fmall membranous and ftraight canal, in a foftifli body fi¬ 
tuated in the fella turcica, named glandula pituitaria. 
This pituitary gland is a fmall fpongy body lodged in the 
fella turcica, betw een the fphenoidal folds of the dura ma¬ 
lt is a Angular kind of fubftance, and feems to be neither 
medullary nor glandular. On the outfide it is partly grey¬ 
ifli and partly reddifli, but white within. The tubercles 
are four in number, two anterior and two pofterior. They 
are tranfverfely oblong, the anterior being a little more 
rounded, and broader or larger from before backward, 
than the pofterior; their furface is white, and their inner 
fubftance greyifli. The names of nates and tefes, given 
by the ancients to thefe tubercles, are not very proper, 
there being little refemblance between them and the things 
from which the names are taken. Some of the moderns, 
with perhaps (fill lefs propriety, have called them tuber - 
cula quadrigemina. Dircitly under the place where the 
tubercles of one fide are united to the tubercles of the 
other fide, lies the iter ad quartum ventriculum, which 
communicates, by its anterior opening, with the third 
ventricle, under the thalami nervorum opticorum, and, 
by its pofterior opening, with the fourth ventricle, which 
belongs to the cerebellum. Where the convex parts of 
the two anterior tubercles join thefe pofterior convex parts 
of the thalami nervorum opticorum, an interftice or o- 
pening is left between thefe four convexities ; but it does 
not communicate with the third ventricle, for the bottom 
of it is fhut up by the pia mater. The name of anus is 
applied to it. The glandula pinealis is a fmall foft greyifh 
body, about the fize of an ordinary pea, irregularly round, 
and fometim.es of the figure of a pine-apple, fituated be¬ 
hind the thalami nervorum opticorum above the tubercula 
quadrigemina. It is fixed like a fmall button to the low¬ 
er part of the thalami, by fivo very white medullary pe- 
dunculi, which, at the gland, are very near each other, 
but feparate almoft tranfverfely toward the thalami. It 
feems to be moftly of a cortical fubftance, except near 
the footftalks, where it is fomewhat medullary. This 
gland 
