308 DB. A. KEITH ON THE CHIMPANZEES. [Mar. 7, 



It will be thus seen that there is scarcely a feature in any 

 muscle or any bone in the body of the Chimpanzee or Gorilla that 

 can be said to be distinctive, and yet, when their characters are 

 summed up, on an average, there are very striking differences 

 between the body of the one and the body of the other. 



7. The External Ear of the Gorilla and Chimpanzee, 



The external ear of Man and the Anthropoid Apes, as well as that 

 of some South- American monkeys, is in a retrograde phase of de- 

 velopment. Retrogression has proceeded furthest in the ear of the 

 Orang-utan, to a Jess degree in the ears of Man and the Gorilla, 

 and least in that of the Chimpanzee. " Johanna " has what may 

 be described as the typical Chimpanzee ear, a form not known to 

 occur amongst Gorillas. It measures 85 mm. from the top of the 

 helix to the lower border of the lobule, and 50 mm. from the base 

 of the tragus to the posterior border of the helix. The height of 

 the Gorilla ear seldom exceeds 60 mm. and its breadth is commonly 

 about 40 mm. The ear of the Chimpanzee stands out from the 

 side of the head at an angle, like the wind-sail from the port-hole 

 of a steamer ; the ear of the Gorilla is appressed to the side of the 

 head. Du Chaillu describes the ear of A. kooloo-Jcamha as very 

 large ; the ear of A. aiibryi, supposed to be of this species, was 

 much smaller than that of " Johanna " ; while the ear of " Mafuka " 

 resembled in size that of the Gorilla. The small. Gorilla type of 

 ear is seen occasionally in the Chimpanzee. The Chimpanzee type 

 of ear is quite a common human form. The folding of the poste- 

 rior border of the ear, which must be regarded as evidence of a 

 retrograde development, has proceeded to a further extent in the 

 Gorilla than the Chimpanzee. 



The degree to which the posterior border of the Helix is folded 

 in Gorillas and Chimpanzees. 



Number. Not folded. 2 mm. fold 4 mm. fold Average, 



or less. or less. 



Gorillas 19 2 15 5 1-30 



Chimpanzees . . 22 9 12 1 -60 



The lobule of the ear is more developed in the Gorilla. 

 "Johanna" possesses a very large lobule, measuring about 12 mm. 

 in depth. 



The development of a Lohule in Gorillas and Chimpanzees. 



Total Lobule less than Less than More than Average, 

 number, 10 mm. deep. 15 mm. deep. 15mm. deep. 



Gorillas 25 4 16 5 10-4mm. 



Chimpanzees. 14 9 4 1 3*4 mm. 



The average development of the lobule of the human ear is 

 nearly 15 mm. Its meaning is unknown. 



