200 ME. r. E. BEDDAED— CONTEIBUTIONS TO THE 



It is evident, therefore, that much stress cannot be laid upon this alleged difference 



between Man and the Chimpanzee. The following measurements will show these 



differences more clearly : — 



Total length of cerebrum Length between anterior 



measured from above a end of cerebrum and 



vertical plate at each end point of V in fissure 



and covering the cerebrum. of Eolando. 



mm. mm. 



Troglodytes calvus 100 54 



„ niger (a) 98 62 



„ niger (b) ....,• • 96 57 



The fissure of Rolando in the brain of the Bald-headed Chimpanzee has the same 

 two anterior connections that it has in the common species ; its shape is that of the 

 letter W; the innermost convexity is, however, much more marked than in either of 

 the two Chimpanzees' brains with which I have compared it. As to the other fissures, 

 they show such variation in individuals that I do not think a detailed description of 

 one brain will serve any useful purpose. I therefore direct attention to the accom- 

 panying drawings (Plate XXIII.) of the brain, which will be of more assistance to 

 investigation in the future than any description. 



The under surface of the brain shows one noteworthy difference between the two 

 species of Chimpanzee. In the Common Chimpanzee the frontal lobes are, as in the 

 lower Apes, keeled below in the middle ventral line, looking as if they had been 

 artificially pressed together by the thumb and forefinger. There was hardly any sign 

 of this in Troglodytes calvus, and in this particular the brain is more like that of the 

 Orang. 



The interval between the temporo-sphenoidal lobes was very much less in Troglo- 

 dytes calvus than in the Common Chimpanzee, not very much more than one half. 

 This is partly due to the position of the lobes in question, and is correlated of course 

 with the more vertical direction of the Sylvian fissure already referred to. The 

 apex of the temporo-sphenoidal lobes is decidedly less blunt than in the Common 

 Chimpanzee. 



The posterior aspect of the brain is also characteristic. The lateral masses of the 

 cerebellum (Plate XXVIII. figs. 1, 2) come into contact behind, overlapping the 

 median tract, which they largely conceal. This is precisely what occurs in the Orang, 

 but not in Troglodytes niger. In that Chimpanzee (Plate XXVIII. fig. 2) the median 

 tract of the cerebellum is not concealed by any overgrowth of the cerebellar hemi- 

 spheres. The peculiar form of this region of the cerebellum, as compared with that 

 of the Common Chimpanzee, will be best appreciated by a comparison of figs. 1 and 2 

 of Plate XXVIII. , which represent the posterior aspect of the brain of " Sally " and 

 of one of the two Common Chimpanzees belonging to the Prosector's stores. 



