ANATOMY. 
99 
I see- streaks of different colours, like those of 
!«j the corpora striata. 
These two eminences are closely joined to- 
! gether; and at their convex part they are so 
far united, as really to become one body; the 
whitish outer substance being continued uni- 
formly over them both. 
Third ventricle. Immediately under the 
I union, or beginning of the thalami nervorum 
jf opticorum, lies a particular cavity, called the 
I third ventricle of the cerebrum. This cavity 
I communicates, at its upper and fore part, 
| with the passage between the two lateral ven- 
j tricles, and sends down from its under and 
I I fore part a passage through the infundibulum. 
I It opens backward into the passage called toe 
iter ad quartum ventriculum. 
Infundibulum. Between the basis of the 
anterior pillar of the fornix, and the anterior 
part of the union of the optic thalami, lies a 
jj small medullary canal, named infundibulum. 
| It runs down toward the basis of the cerebrum, 
I contracting gradually, and terminates in a 
| straight course by a small membranous canal, 
| in asoftish body, situated in the sella Turcica, 
i* named glandula pituitaria. 
Plexus choroides. The plexus chorokk s is 
la very fme vascular texture, consisting of a 
| great number of arterial and venal ramifica- 
| tions, partly collected in two loose vasculi, 
| which lie on each lateral ventricle, and partly 
I expanded over the neighbouring parts, and 
I covering in a particular manner the thalami 
| nervorum opticorum, glandula pineal is, tu- 
$ bercula quadrigemina, and the other adjacent 
| parts, both of the cerebrum and cerebellum, 
| to all which it adheres. 
Glandula pituitaria. The pituitary gland 
| is a small spongy body, lodged in the sella 
f Turcica, between the sphenoidal folds of the 
l dura mater. On the outside it is partly grey- 
I ish, and partly reddish, and white within. It 
I is transversely oval or oblong ; and on the 
I lower part, in some subjects, is divided by 
I a small notch in two lobes, like a kidney- 
1 bean. It is covered by the pia mater, as by 
I a bag, the opening of which is the extremity 
l of the infundibulum : and is surrounded by 
I the small circular sinuses, which communicate 
I with the sinus of the cavernosi. 
Tubercula. The tubercles are four in 
I number, two anterior and two posterior; ad- 
I bering together, as if they made but one 
I body, situated behind the union of the thalami 
1 nervorum opticorum. They are transversely 
■ oblong, the anterior being a little more round- 
led, and broader, or larger, from before back- 
I ward than the posterior. Their surface is 
I white, and their inner substance greyish. 
I ® D.rectly under the place where the tuber- 
cles of one side are united to those ot the 
other side, lies iter ad quartum ventriculum, 
which communicates by its anterior opening 
with the third ventricle, under the thalami 
nervo. urn opticorum, and by its posterior 
opening with the fourth ventricle, which be- 
longs to the cerebellum. 
! Foramen commune posterius, where the 
convex parts of the two anterior tubercles join 
these posterior convex parts of the thalami 
nervorum opticorum, an interstice, or open- 
ing, is left between these four convexities ; but 
it does not communicate with the third ven- 
tricle, for the bottom of it is shut up by the 
pia mater. It has got the name of anus ap- 
Splied to it, 
i Glandula pinealis. The glandula pineal is 
is a small, sott, greyish body, about the size 
of an ordinary pea, irregularly round, and 
sometimes of the figure ot a pine-apple, situ- 
ated behind the thalami nervorum opticorum, 
above the tubercula quadrigemina. it is fixed 
like a small button to the lower part of the 
thalami, by two very white medullary peduu- 
cuii, which at the gland are very near each 
other, but separate transversely towaid the 
thalami. 'Phis gland is almost always found 
to contain a peculiar gritty substance : below 
the glandula pinealis there is a medullary 
tranverse cord, called the posterior commis- 
sure of the hemispheres of the cerebrum. 
Cerebellum. 
Situation and figure. The cerebellum is 
contained under the transverse septum of the 
dura mater, in the under and back part of the 
cranium. It is broader laterally than on the 
fore or back sides, flatted on the upper side, 
and gently inclined both ways, answerable to 
tiie septum, which serves it as a kind of tent 
or ceiling. On the lower side it is rounder ; 
and on the back side it is divided into two 
lobes, separated by the occipital septum of 
the dura mater. 
Structure. It is made up like the cere- 
brum, of two substances. It has two middle 
eminences, called appendices vermiformes : 
one anterior and superior, and turned for- 
ward ; the other posterior and inferior, which 
goes backward. There are likewise two la- 
teral appendices, both turned outward. They 
are termed vermiformes, from their resem- 
blance to a large portion of an earthworm. 
Fourth ventricle. When we separate the 
two lateral portions or lobes, having first made 
a pretty deep incision, we discover first of all 
the posterior portion of the medulla oblon- 
gata, of which hereafter: and in the posterior 
surface of this portion, from the tubercula 
quadrigemina, all the way to the posterior 
notch, in the body of the cerebellum; and a 
little below that notch, we observe an oblong 
cavity, which is called the fourth ventricle ; 
this terminates backward, like^the point of a 
writing pen. Hence the under end of it is 
called calamus scriptorius. If we cut one 
lobe of the cerebellum vertically, from above 
downward, the medullary substance will ap- 
pear to be dispersed in ramifications, through 
the cortical substance. These ramifications 
have been named arbor vita?, and the two 
trunks, whence these different lamina: arise, 
are called pedunculi cerebelh. 
Medulla oblongata. 
The medulla oblongata is a medullary sub- 
stance, situated from before backward in the 
middle part of the basis of the cerebrum and 
cerebellum, without any discontinuation be- 
tween the lateral parts of both these bases. 
The chief medullary productions are these ; 
the large, or anterior branches of the medulla 
oblongata, which have likewise been named 
crura anteriora medulla: oblongata?, and pe- 
dunculi cerebri ; the transverse protuberance, 
called likewise processus annularis, or pons 
Varolii ; the smaller posterior branches, call- 
ed pedunculi cerebelli, or crura posteriora 
medulla; oblongata? ; the extremity, or cauda, 
of the medulla oblongata, with two pairs of 
tubercles ; one of which is named corpora 
olivaria, the other corpora pyramidaiia ; and 
to all these productions we must add a pro- 
duction of the infundibulum, and two medul- 
lary papillae. 
Medulla spinalis. 
The medulla spinalis is only an elongation 
of the extremity of the medulla oblongata, 
and it lias its name from its being contained in 
the bony canal of the spina dorsi. It is con- 
sequently a continuation or common appen- 
dix of the cerebrum and cerebellum, as well 
because of the two substances of which it is 
composed, as because of the membranes by 
which it is invested. 
NEUROLOGY. 
Of the Nerves in general. 
The continuity of the cortex with the me- 
dulla of the encephalon and spinal marrow is 
observable with the naked eye, and is more 
distinctly seen with the assistance of a micro- 
scope. In dissecting the brain and cerebel- 
lum, we see the small beginnings of the me- 
dulla proceeding from the cortex, and can 
trace its gradual increase by the addition qf 
more such white substance coming from the 
cortex. Both these substances are very suc- 
culent ; for being exposed to the air to dry, 
they lose more of their weight than most 
parts of the body do. 
In several places we can observe the me- 
dulla to be composed of fibres laid at each 
other’s sides ; and it is employed in forming 
the white fibrous cords, which have now tke 
name of nerves appropriated to them. With- 
in the skull we see the nerves to be the me- 
dullary substance continued, and the spinal 
marrow is employed in forming all nerves. 
The common opinion concerning the use 
of the nerves, founded on a superficial inspec- 
tion of those parts, is, that the nerves are pro- 
pagated from that side of the encephalon 
at which they go out of the skull. But it 
having been remarked, after a more strict en- 
quiry, and preparing the parts by maceration 
in water, that the medullary fibres decussate 
or cross each other in some parts of the me- 
dulla, as, for example, at the corpus annu- 
lare, and beginning of tire spinal marrow ; 
and practical observations having related se- 
veral examples of people whose brain was 
hurt on one side, while the morbid symp- 
toms, palsy, appeared on the other side of 
the body, of which we have seen some in- 
stances; and experiments on brutes having 
confirmed these observations, it has been 
thought that the nerves had their rise from 
that side of the encephalon which is opposite 
to their egress from the skull. It may, how- 
ever, still be said, that this last opinion is not 
fully demonstrated, because a decussation in 
some parts is not a proof that it obtains uni- 
versally ; and if there are examples of palsy 
of the side opposite to where the lesion of tin* 
brain was, there are also others, where the 
injury done to the brain and the palsy were 
both on the same side. 
The nerves are composed of a great many, 
threads ly ing parallel to each other, or ne wly 
so, at their exit from the medulla. This 
fibrous texture is evident at the origin of 
most of the nerves within the skull; and in 
the cauda equina of the spinal marrow, we 
can divide them into such small threads, that 
a very good eye can scarce perceive them : 
but these threads, when looked at with a mi- 
croscope, appear each to be composed of a 
great number of smaller threads. How small 
one of these fibres of the nerve is, we know 
not ; but when we consider that every, even 
the most minute, part of the body 'is se*-> 
