656 



STRUCTURE OF THE CEREBRUM. 



[OH. XLVI. 



callosum which unites the hemisphere to its fellow. The sub- 

 division into lobes is not so apparent here as on the external 

 surface of the hemisphere, so we may pass at once to the convo- 

 lutions into which it is broken up by fissures. 



u g B c 



-MPORAL 

 Fig. 488. Eight cerebral hemisphere, mesial surface. 



In the middle the corpus callosum is seen cut across ; above 

 it and parallel to its upper border is a fissure called the calloso- 

 marginal fissure which turns up and ends on the surface near 

 the upper end of the fissure of Rolando. The convolution above 

 this is called the marginal convolution, and the one below it the 

 callosal convolution or gyrus fornicatus. The deep fissure below 

 the corpus callosum running from its posterior end forwards and 



downwards is called the dentate 

 fissure ; this forms a projection 

 seen in the interior of the lateral 

 ventricle and called there the 

 hippocampus major; it is some- 

 times called the hippocampal con- 

 volution which, together with the 

 gyrus fornicatus above the corpus 

 callosum, constitutes the limbic 

 lobe. Below the dentate fissure 

 is another called the collateral 

 fissure, above which is the uncinate 

 convolution, and below which is 

 the inferior temporal convolution 

 which we have previously seen on 

 the external surface of the hemisphere (see fig. 487). In the 

 occipital region the internal parieto-occipital fissure, which is a con- 

 tinuation of the external parieto-occipital fissure, passes downwards 

 and forwards till it meets the calcarine fissure ; these two enclose 

 between them a wedge-shaped piece of brain called the cuneus or 



A.P.S 



Fig. 489. Orbital surface of frontal lobe. 

 M, marginal convolution. 



0, olfactory sulcus. 

 O.S., orbital sulcus. 



1, island of Reil. 



S.a, anterior limb of Sylvian fissure. 

 S.p, posterior limb of Sylvian fissure. 

 A.P.S. , anterior perforated spot. 



