ANATOMY. 



upon its surface in minute vessels. The 

 outer surface is tolerably smooth ; the 

 inner universally villous, from the torn 

 orifices of innumerable vessels, which en- 

 tered the substance of the brain. 



The surface of the brain appears con- 

 voluted, so as to resemble the windings of 

 the small intestines. These convolutions 

 do not in general penetrate more than 

 one inch, or an inch and a half, into the 

 substance. 



The contents of the cranium are divid- 

 ed into cerebrum, cerebellum, and medul- 

 la oblongata. 



The cerebrum is the upper, and by far 

 the largest, portion : it occupies all the 

 superior part of the vaulted cavity of the 

 skull, and rests below on the tentorium, 

 the petrous portions of the temporal 

 bones, the sphenoid alae, and the orbits. 

 Its upper surface presents a regularly 

 convex oval, narrower in front} than be- 

 hind. It is divided into a right and left 

 hemisphere by a deep longitudinal fis- 

 sure, into which the falx cerebri descends. 

 Each hemisphere is divided into two 

 lobes by means of the fissura magna Syl- 

 vii. This fissure commences at the basis 

 of the brain, opposite to the lesser ala of 

 the sphenoid bone ; the anterior lobe is 

 that portion of the hemisphere situated 

 in front of the fissure ; and the posterior 

 lobe is the division placed behind. 



The hemispheres of the cerebrum are 

 united together at about two inches and 

 a half from the surface of the brain, by 

 means of a medullary body, called corpws 

 callosum. This is about three inches in 

 length, and three quarters of an inch in 

 breadth. 



As there are no distinguishable parts in 

 the upper portions of the hemispheres 

 of the cerebrum, it is customary to pare 

 all these away in dissection, nearly to the 

 level of the corpus callosum, in ,order 

 that we may be able more easily to open, 

 and more particularly to examine, certain 

 cavities, which are situated at the sides of 

 that body, and are called the lateral ven- 

 tricles. 



On making a section of the brain, we 

 perceive that it is composed of two sub- 

 stances ; an exterior one, which is of a 

 grey colour, and an interior one, which is 

 white. These are simply termed the ci- 

 neritious and white substances, or sub- 

 stantia cinerea et alba ; or, from the for- 

 mer surrounding the latter, as the bark 

 does the wood of a tree, they are named, 

 in contradistinction, the cortical and me- 

 dullary substances of the brain. 



The two lateral ventricles are situated 



in the substance of the brain, by the side 

 of the corpus callosum, (one in either he- 

 misphere.) 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 direc- 

 tion parallel to that body, and at its poste- 

 rior end bends dow n \vards,and returns ob- 

 liquely from behind forwards, to terminate 

 almost under its superior extremity. At 

 the place where the ventricle bends, in 

 order to run downwards, there is a parti- 

 cular elongation passing into the posterior 

 lobe, 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 

 ventricies of the brain contain a small 

 quantity of a watery fluid. The disease of 

 h} drocephalus is a- morbid increase of 

 quantity in this fluid, which accumulates 

 sometimes to the amount of some pounds, 

 distending and dilating the ventricles 

 enormously. The learned Soemmering, 

 who may justly be esteemed the first of 

 modern anatomists,. places the censorium 

 commune in this fluid. He has traced all 

 the nerves of the brain to the sides of the 

 ventricles; and concludes, that impres- 

 sions made on these nerves will be trans- 

 mitted to the water of the ventricles, 

 which he considers as the organ of the 

 soul. 



The two lateral ventricles are separated 

 by a perpendicular partition, called the 

 septum lucidum,. which passes from the 

 corpus calloaum to the fornix. It contains 

 a small triangular cavity, called by some 

 the fifth ventricle of the brain. It has no 

 communication with the other cavities of 

 the brain. 



The fornix is a roundish medullary bo- 

 dy, lying between the two ventricles at the 

 lower part. It arises by two anterior crura 

 from the 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 arterial and venous ramifications, float- 

 ing almost loosely in the cavity of the ven- 

 tricles. It is first observed in the reflect- 

 ed portion of the ventricle, where it is the 

 broadest and largest : it diminishes in size 

 as it ascends/ and terminates just at the 

 opening of communication between the 

 two cavities. The choroid plexuses of the 

 t\vo ventricles are united bv a middle ex- 



