30 Dr. Foville on the Anatomy of the Brain. 



in each posterior half of the hemispheres, are in accordance 

 with these peculiarities. To this region correspond the 

 convolutions situated behind the posterior margin of the 

 corpus callosum as far as the posterior termination of the 

 ventricles. 



Lastly, the fourth region, situated in the interval between 

 the superior occipital protuberances and the upper curved 

 line of the occiput, divides the latter into a median convex 

 quadrangle, and two lateral triangles, whose pointed summits 

 terminate near the mastoid process. Now these triangles, 

 instead of being convex like the rest of the median arch, al- 

 most always present a plain or even concave surface. The 

 depressed portions of these triangles correspond at their 

 sharp summits to the insertion of the tentorium cerebelli and 

 the external part of the lambdoidal suture. 



In the temporal regions of the cranial arch, we always re- 

 mark, on a level with the great wing of the sphenoid bone, a 

 depression running upwards and backwards in the same 

 direction as the fissure of Sylvius, to which it corresponds. 

 A right line drawn from the top of this depression towards 

 the centre of the parietal eminence, marks the course of the 

 fissure of Sylvius, and allows us to measure, on the living 

 subject, the comparative volume of cerebral substance situated 

 in front, and of that behind, this fissure. 



Now the fissure of Sylvius, and the cranial depression 

 answering to it at the fore part of the temporal fossa, are 

 variously modified according to the modifications of the ven- 

 tricular hollow. The anterior and temporal regions of these 

 cavities are separated by a large nervous mass which follows 

 the crus cerebri. The fore part of the ventricle is enlarged 

 above this mass and the temporal part of the ventricle be- 

 low it. 



The fissure of Sylvius, then, forms the interval between 

 two regions of the ventricle, the frontal and the temporal, 

 and consequently the interval between the convolutions co- 

 vering in these two distinct regions of the serous cavity. It 

 ceases above, at the part where these regions of the ventri- 

 cular cavity unite into a common conflux. Its deepest part 

 is below, at the bottom of the widest interval between the 

 frontal and temporal extremities of the ventricle. 



Thus the form of the brain, and that of the skull also, 

 would seem to be determined in their general character by 

 the form of the serous sacs inclosed in the hemispheres, and 

 constantly filled with the fluid peculiar to them. 



This is not meant to imply that the cerebral convolutions 

 do not exert any influence on the secondary shape of the 



