364 NERVOUS SYSTEM. 



The middle line of its upper surface is marked out from one 

 end to the other by a very slight depression, the Raphe; on 

 each side of which there is a very small linear elevation of the 

 same extent, but slightly curved inwards towards its fellow. 

 From these longitudinal lines there proceed outwardly trans- 

 verse ones, having a fibrous appearance. At the anterior and 

 posterior ends of the corpus callosum, the latter are some- 

 what curved and radiated towards the periphery of the brain. 

 Other longitudinal lines also exist on the surface of the corpus 

 tallosum, hut they are not seen with equal facility. The an- 

 terior extremity of the corpus callosum is rounded off, and bent 

 downwards towards the basis of the brain, in such a manner 

 as to present backwards its concavity; which thus embraces 

 the fore part of the corpora striata, and closes the lateral ven- 

 tricles at this point, The posterior end of the corpus callosum 

 is rounded, also, and continuous with the fornix and with the 

 cornu ammonis. 



By examining the Corpus Callosum from below, or by look- 

 ing at its relative situation and shape on a hemisphere which is 

 accurately separated from its fellow in the middle line, it will 

 be seen that its lower surface is very concave, being highly 

 arched from before backwards; that it forms the roof of the la- 

 teral ventricles, and that this surface of it is about two inches 

 in its transverse diameter, and, therefore, more than twice as 

 broad as the upper surface. 



The Fornix, (Trigone Cerebral, of the French) is placed im- 

 mediately below the corpus callosum. It is a triangular body 

 of medullary neurine or matter, the base of which is behind 

 and the apex in front. It is about an inch and a half long in 

 its body, and one inch wide at its base. It is the latter part, 

 which, lying immediately beneath the posterior end of the cor- 

 pus callosum, is continuous with it, and causes the fornix to be 

 considered as a part of the same structure with the corpus cal- 

 losum. These two bodies, which may be compared to a sheet 

 of medullary matter doubled on itself, have their surfaces in 

 contact for a short distance behind, the fornix afterwards, by 

 advancing and keeping itself in close contact with the thalami 

 nervorum opticorum, which are just below it, diverges more 

 and more from the under surface of the corpus callosum. It 



