16 EINAR LONNBEEG, MAMMALS COLLECTED IN CENTRAL AFRICA. 



The young male with milk-dentition (n:o 166) 470 ccm. 



» » » » m' and m, (n:o 40) 465 !• 



The semiadult male (n:o 165) 597 » 



The old male (n:o 164) 585 j 



These measurements prove in the first rank that the female brain is much smaller 

 than the male one which, of course, at least partly stands in direct relation to the differ- 

 ence in bodily size of the two sexes. Nevertheless it is of great interest to find that the 

 young male in milk-dentition, which has not yet by far attained so great bulk as the adult 

 female^, already is her considerably superior with regard to the volume of the brain-cavity. 

 It is also rather astonishing to find that the young female Gorilla still in milk-dentition^ 

 has a brain-cavity which is nearly as great as that of the adult female, or 94 % of the 

 same, although the difference in size between the specimens is considerable. This fact 

 appears to indicate that the brain of the female Gorilla grows to nearly its definite size 

 pretty early, but then comes to a standstill. 



The brain-cavity of the young male Gorilla in milk -dentition and that of the young 

 male with the first molars developed' is practically the same. That the latter even is a 

 little smaller is no doubt a case of individual variation without importance. During the 

 period of life in which the second and third molars come to full development the brain 

 of the male Gorilla, unlike that of the female, appears to be subjected to vigorous increase 

 in size, as may be concluded from the fact that the brain of the semiadult male is so very 

 much larger than that of the younger specimens. The capacity of the brain-cavity of the 

 younger males is only 79 %, or less of that of the semiadult. But in that semiadult 

 stage the brain of the male Gorilla appears to have attained its full size. Whether it 

 actually decreases again with age as the above measurements appear to indicate, or not, 

 is difficult to decide, as the difference in this direction, expressed above, may be due only 

 to individual variation. The growth of the Gorilla brain is, as it will appear, periodical. 



The female Gorilla child n:o 168 and the male n:o 166 appear to be of almost the 

 same age to judge from the development of the teeth and the skull, although the female 

 skin is larger, and this specimen thus is older. The brain capacity of the female is, how- 

 ever, only about 88 % of that of the male, which fact thus proves that the superiority of 

 the males in this respect is pronounced at a rather early period, and it is increased still 

 more with age as is shown above. 



Sblbnka has in his valuable memoir »Menschenaffen (Anthropomorphse), Studien 

 liber Entwicklung und Schadelbau »" published measurements of the capacity of the brain- 

 cavity of 48 female and 60 male Gorillas, all adult. In the females the capacity varies 

 according to Selbnka between 380 and 530 ccm. with an average volume of 450 ccm. The 

 female Mikeno Gorilla has thus a brain cavity which is somewhat below the average. 

 According to the same author the capacity of the brain-cavity of the male Gorillas varies 

 between 420 and 590 ccm. with an average of 510 ccm. The male Mikeno Gorillas reach 



1 The length of the skin from upper lip to vent is about 57 cm. in the former but 104 cm. in the latter. 

 ' Length of the skin measured as above 67 cm. 

 ' Length of the skin about 86 em. 

 4 Wiesbaden 1898—1900. 



