1899. DR. A. KEITH ON THE CHIMPANZEES. 301 



The palate of the Central-African Chimpanzee most resembles 

 that of the Gorilla. The average area for 3 males amounted 

 to 4350 c.c, rather less than the ordinary Chimpanzee ; the breadth 

 is only 71 per cent, of the length — a very low amount. The skulls 

 of Anthrojiopithccus calvus and A. hooloo-hamba are too few to draw 

 inferences from, but in both the breadth index is over 80 per cent. 



The difference in form and size of the teeth of Grorillas and 

 Chimpanzees is very emphatically marked. The cusps of the molars 

 of the Gorilla are extremely prominent, almost prismatic, with the 

 enamel deposited in a sharp crystalline manner, with only round 

 the bases of the cusps evidence of the erenated folds of enamel 

 Avhich form a pronounced character in the teeth of Chimpanzees. 

 The cusps of the Chimpanzee are bluntly conical and not nearly 

 so prominent as in the Gorilla. The crenation of the enamel 

 is perhaps the most diagnostic feature of the great Anthropoids. 

 Cusps resembling those of the Gorilla occur in the teeth of the 

 Siamang and some South-American monkeys (BrachyteJes and 

 Lagoihrix), and represent the molar cusp at its most robust de- 

 velopment. The cusps of the Central-African Chimpanzee most 

 resemble those of the Gorilla, but never approach them in degree 

 of development. 



The molar teeth of the Gorilla, as may be seen from the 

 accompanying measurements, are ver}' much larger than those of 

 the Chimpanzee : — 



m.^ m.^ m.^ m.'- m.-^ m.^ 



Length of Diolar teeth, ) 

 stated in mm., an average 1 14-6 (X 14) 15-2 14-1 15 16 17 



of both sexes of Gorilla... J 



Do. Chimpanzee 10 (x 10-5) 10-2 8 11-5 12 11 



One may say, almost with certainty, that any upper molar tooth 

 over 12 mm. in length is that of a Gorilla, and under 12 is that of 

 a Chimpanzee. The molar teeth of the female (xorilla are almost 

 as large as tliose of the male : the molars of the female Chimpanzee 

 are smaller than those of the male and show more marks of retro- 

 gression : while the third molar of the Gorilla, especially the lower, 

 is as fully developed as the other two teeth, the corresponding 

 tooth in the Chimpanzee, as in Man, and as in the Orang, shows 

 distinct retrograde changes. The table on p. 302, the result of the 

 examination of 22 Gorilla and 26 Chimpanzee skulls, shows the 

 retrograde development of the cusps in the Cliimpanzee, especially 

 in the third molar tooth. 



The observations show that in point of size, in development of 

 cusps, and in arrangement of enamel the teeth of the Gorilla far 

 exceed those of the Chimpanzee, and, unlike former points of 

 difference, the distinction between the molars of the females is as 

 well drawn as between the molars of the males. 



In every point the teeth of the Central-African Chimpanzee 

 make the nearest approach to the Gorilla ; the molars of the Bald 

 Chimpanzee have probably undergone the most retrograde change. 



