:moupiiologt of the brain ix the mammalia. 



3G3 



uiilila' the latter, but the extreme broadeuiug' of the hemisphere ijosteriorly ami the 

 more pronounced tapering of its anterior part give the brain (as a whole) an oval form, 

 which is quite unlike that of Lemur. Porsyth Major compares its shape to that of 

 Jlicrocebits ; oa the whole I think that the dorsal contour of the brain api)roaches 

 nearest to that of the smaller Cercopithecidse. 



Fig. 40. 



Pig. ."39. — (•Johthmur Flarmirti. Tlie dorsal aspect of a cranial cast. x :\. 

 Fig. 40. — Gloliilemur F/acoiirti. The left lateral aspect of the same. x ,j. 



The problem of mapping-out the pattern of the cerebral sulci in this brain is one of 

 singular and unexpected difficulty. In most Lemurs and in many of the Cebidse the 

 positions and extent of the various sulci can be determined with the greatest ease and 

 certainty. But in the crania of most Apes the ridges which corresjjond to the position 

 of the cerebral furroAvs become blurred and indistinct in the greater part of the surface, 

 excepting only the anterior region, which contains sharply-defined elevations representing 

 the sulci rectus, arcuatus, orbitalis, and fronto-orbitalis. 



If a series of crania of Cercopithecidtie be examined, it will be found in many of i hem 

 that all the ridges behind that representing tlie sulcus arcuatus are so indistinct that it 

 would not be easy to map out the sulci, if we did not liappen to know the plan. It is 

 a i)eculiar iact that the ridge for the Sylvian fissure, which is always so distinct in the 

 Lemurs, becomes almost completely obliterated in the crania of many Ajjcs. And 

 the crests representing the intraparietal, the parallel, and, in a less marked degree, the 

 central sulci share a like fate. 



A similar state of affairs is unfortunately jjreseut in Globllemur ; so that it is quite 

 impossible to map out the position of most of the sulci. As in the Apes, the ridges 

 representing the sulci on the anterior region of the hemisphere are by far the most 

 distinct. 



Tlius there can be no doubt concerning the recognition of the orbital (t^) and coronal (Ij) 

 sulci (figs. 3!J & 40). There is a prominent bony ridge representing a furrow skirting the 

 fronto-orbital margin of tlie hemisphere, wiiich is probably the diagonal sulcus (e). But 

 the determination of the identity of the other furrows offers insuperable difficulties. 



In both hemispheres there is a short vertical furrow (/), which both Forsyth ]\[ajor 

 and Burckhardt consider to be the representative of the Sylvian lissure or part of it. 



