772 



THE NERVOUS SYSTEM. 



that of its fellow by the great longitudinal fissure, which extends throughout the 

 entire length of the cerebrum in the middle line, reaching down to the base of 

 the brain in front and behind, but interrupted in the middle by a broad transverse 

 commissure of white matter, the corpus callosum, which connects the two hemi- 

 spheres together. This fissure lodges the falx cerebri, and indicates the original 

 development of the hemispheres by two lateral halves. 



Each hemisphere presents also an outer surface, which is convex to correspond 

 with the vault of the cranium ; an inner surface, which is flattened and in contact 

 with the opposite hemisphere (the two inner surfaces forming the sides of the 

 longitudinal fissure) ; that is, above, in front of, and below (reflected portion) 

 corpus callosum ; the lower part of the mesial surface (inner aspect of internal 



Splenium 



Part of 

 trans. fissure 



Pin. gland 



Pulvinar of 

 optic thai. 



,Brachium of 

 C tup. c. q. 



j|\ Brachium 

 WL^ inf. c. q. 



Vncus of 

 hipp. gyrus 



IV. N. 

 FIG. 463.-The brain from behind. The hemispheres and 



him are widely separated. (Henle.) 



capsule) resting against and being adherent to outer side of optic thalamus 

 (Fig. 461). 



If the arachnoid and pia mater are removed, the entire surface of each hemi- 

 sphere will be seen to present a number of depressions (fissures and sulci) sepa- 

 rating a number of convoluted eminences (convolutions or gyri}. 



The depressions are of two kinds, fissures and sulci. The fissures are few in 

 number; they are constant in their arrangement, and are produced by marked 

 foldings of the hemisphere during the process of development. There are seven 

 fissure of Sylvius, fissure of Rolando, parieto-occipital, calloso-marginal, hippo- 

 campal, calcarine, and collateral fissures. The first four serve to mark off from 

 each other the larger lobes of the hemisphere i. e. frontal, parietal, temporal, 

 and occipital and also two others, the island of Reil or central lobe, and the 

 limbic lobe. There is still one other lobe, the olfactory. The three last-named 

 fissures cause elevations in the ventricle viz. hippocampus major and minor 

 and eminentia collaterals. 



The sulci are much more numerous ; they are depressions of the gray matter, 

 which is folded inward and only indents the central white substance ; they vary 

 in different brains and in different parts of the same brain. 



