Component Matter of the Brain. [Book 



feems to be compofed of numerous white, minute, 

 parallel, and very tender fibres. 



Having removed the falx from between the hemi- 

 fpheres of the brain, and drawn them gently from each 

 other, we cbferve below a white convex furface, which 

 Is part of what is called the corpus callolum. It is a 

 middle portion of the medullary fubflance, which, un- 

 der the inferior edge of the falx, and for fome diftance 

 on each fide, is parted from the mafs of the cerebrum 

 by a fold of the pia mater. Along the middle of 

 the fur face of the corpus callolum, a kind of fu- 

 ture is formed by a particular intertexture of fibres 

 croffing each other. Immediately under thefe is placed 

 the feptum lucidum, which is connected below to the 

 fornix, and divides the anterior ventricles of the brain 

 from each other. Thefe ventricles are difcovered by 

 making an horizontal incifion in the brain, on a level 

 with the corpus callofum. When we have cut into 

 them, we find that they are narrow canals, which take 

 a very winding courfe through the fubftance of the 

 brain. They are lined with the pia mater, and con- 

 tain a curious collection of minute blood vefiels twifted 

 about each other, and called plexus choroides. One 

 of the anterior ventricles is fituated in each hemifphere 

 of the brain, and they are divided from each other by 

 the feptum lucidum. 



The feptum lucidum is united by its lower part to 

 the anterior portion of that medullary body called the 

 fornix, which forms a kind of arch, fituated under the 

 corpus callofum, and is nearly of a triangular fhape, 

 At the anterior part the fornix fends off a double 

 medullary cord, called its anterior crura; immediately 

 below which we obferve a large white medullary rope 

 ftretched tranfverfely between the two hemifpheres, 

 and commonly called the anterior commiffure of the 



cerebrwn. 



