1899.] DB. A. KEITH OX THE CHIMPANZEES. 303 



enough oE material to make auy statement as to their development 

 in Anthropopitliecus calvus and A. kooloo-lcamha. The premolars of 

 the Chimpanzee although differing in size, do not dii£er much in the 

 number and arrangement of their cusps. 



The canine teeth have attained their greatest development 

 amongst the large Anthropoids in the Gorilla. Their large size 

 expresses the ferocity of the animal. The sexual difference between 

 the canines of the male and female is much greater in the Grorilla 

 than in the Chimpanzee : the canines of the male Chimpanzee 

 equal in their development those of the female Grorilla. The 

 upper canines of the male Gorilla project 14-18 mm. above the 

 other teeth; their antero-posterior diameter varies from 18-20 mm. ; 

 the lower project above the premolar teeth from 8-10 mm. The 

 development of the upper canines of the male Chimpanzee is much 

 less than those of the Gorilla : the upper projects 8-12 mm. with 

 an antero-posterior diameter of 12-15 mm. ; the lower reaches 

 above the other teeth from 4-6 mm. In the female Gorilla the 

 upper canines reach above the other teeth from 8-10 mm. ; the 

 corresponding measurement in the Chimpanzee is from 6-8 mm. : 

 in the lower teeth, the canines of the Gorilla project 4-6 mm. ; in 

 the Chimpanzee seldom more than 3 mm. The size of the canine 

 teeth helps in the diagnosis of the Chimpanzee. 



The incisor teeth of the Gorilla are a fourth larger than those 

 of the Chimpanzee, but the relative size of the individual incisors 

 is almost the same. The upper lateral incisors, owing to the great 

 size of the canines, are relatively small in the Gorilla. The 

 arrangement of the cuspules of enamel on the teeth of the one 

 is different from that of the other, but the small amount of 

 material at my disposal precludes me from making any more 

 definite statement. 



In both the Chimpanzee and Gorilla the last permanent and 

 canine teeth commonly cat together ; but in the Chimpanzee the 

 canine cuts more frequently before the last molar than in the 

 Gorilla. 



" Johanna " has the habit of yawning frequently, when a full 

 view is got of her teeth, and there cannot be a doubt for an 

 instant that in every point she possesses the dentition of a female 

 Chimpanzee. 



I know of four instances of supernumerary molars in the Gorilla. 

 I know of only one in the Chimpanzee, and yet Chimpanzee skulls 

 are three times more numerous than those of the Gorilla. 



6. The Myological and Osteological Differences in the Bodies and 

 Limbs of the Gorilla and Chimpanzee. 



It is a very remarkable fact, and one that very forcibly proves 

 the close relationship between the Gorilla and Chimpanzee, that 

 there is scarcely a feature in any muscle or bone found in one 

 animal which is not also found in the other. What is the ex- 

 ception in the one, frequently proves the rule in the other, and 



