ANATOMY. 
latter, as the bark does the wood of a tree, 
they are named, in contradistinction, the 
cortical and medullary substances of the 
brain. 
The two lateral ventricles are situated in 
the substance of the brain, by the side of 
the corpus caljosum, (one in either hemis- 
phere). The cavity begins in the front 
lobe of the brain, as far forwards as the 
commencement of the corpus callosum ; it 
runs from before backwards in a direction 
parallel to that body, and at its posterior 
end bends downwards, and returns oblique- 
ly from behind forwards, to terminate al- 
most under its superior extremity. At the 
place where the ventricle bends, in order to 
run downwards, there is a particular elonga- 
tion passing into the posterior iobe, forming 
a triangular-pointed cavity, and terminating 
in a cul de sac. This is the digital cavity, 
or cornu posterius of the lateral ventricle. 
These and the other ventricles of the brain 
contain a small quantity of a watery fluid. 
The disease of hydrocephalus is a morbid 
increase of quantity in this' fluid, which ac- 
cumulates sometimes to the amount of some 
pounds, distending and dilating the ventri- 
cles enormously. The learned Soemmer- 
ring, who may justly he esteemed the first 
of modern anatomists, places the sensorium 
commune in this fluid, lie has traced all 
the nerves of the brain to the sides of the 
ventricles ; and concludes, that impressions 
made on these nerves will be transmitted to 
the water of the ventricles, which he consi- 
ders as the organ of the soul. 
The two lateral ventricles are separated 
by a perpendicular partition, called the sep- 
tum lucidum, which passes from the corpus 
callosum to the fornix. It contains a small 
triangular cavity, called the fifth ventricle 
of the brain. 
The fornix is a roundish medullary body, 
lying between the two ventricles at the 
lower part. It arises by two anterior crura 
from tile front of the brain ; these unite to 
form the body or pillar of the fornix, which 
separates behind into two posterior crura, 
that run into the reflected portion of the 
ventricles. Under the anterior part of the 
fornix is a small slit-like opening, by which 
the two lateral ventricles communicate. 
The choroid plexus is a production of the 
pia mater, containing a vast number of ar- 
terial and venous ramifications, floating al- 
most loosely in the cavity of the ventricles. 
It is first observed in the reflected portion 
of the ventricle, where it is the broadest 
and largest: it diminishes in size as it as- 
VOL. 1. 
Cends, and terminates just at the opening of 
Communication between the two cavities. 
The choroid plexuses of the two ventricles 
are united by a middle expansion passing 
under the fornix, and called the velum. 
The lateral ventricle contains certain emi- 
nences, which form its sides; the corpus 
striatum is the anterior and superior emi- 
nence, grey on its external surface, and 
striated internally. The posterior eminence- 
in each ventricle is called the thalamus 
nervi optici ; it is hemispherical, and white, 
and joined to its opposite one by an union 
of substance, called the soft commissure. 
The hippocampus major is a large elongated 
eminence lying in the descending portion of 
the lateral ventricle : and the hippocampus 
minor is a smaller one in the digital cavity. 
The pineal gland, or conarium, is found 
behind the optic thalami. Its size is about 
that of a small horse-bean ; its colour grey, 
and figure conical. Two small medullary 
chords connect it to the optic 4 thalami. In 
the substance of this body is found a small 
quantity of a gritty matter, nearly resem- 
bling sand. It consists of a number of se- 
mi-transparent and light yellow grains. 
Soemmerring, who first discovered that this 
belonged to the healthy structure of the 
brain, calls it the acervulus of the pineal 
gland. This little body has been more at- 
tended to and noticed than it would other- 
wise have been, in consequence of the 
chimerical dream of Descartes, who repre- 
sented it as the seat of the soul. 
Below the pineal gland is a square por- 
tion of the brain, divided into four superfi- 
cial eminences, called corpora quadrige- 
mina, and from these a thin production ex- 
tends to the cerebellum, under the name, of 
valvula cerebri. 
By drawing asunder the optic thalami, 
and separating their soft commissure, we 
expose the third ventricle of the brain. 
This appears as an oblong cavity, about an 
inch and a quarter in length. A round me- 
dullary rope is seen in front of it, and a si- 
milar one behind ; these are called the an- 
terior and posterior commissures. A round 
aperture is observed under the anterior 
commissure, beyond which the ventricle 
terminates by a pointed and conical extre- 
mity, from which a short process is ‘conti- 
nued to tile pituitary gland, under the 
name of infundibulum. The foramen com- 
mune anterius is an opening observed be- 
tween the optic thalami before they are 
disturbed, and leading from the aperture of 
communication, which connects the two la- 
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