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Show 308 DR. 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 development. Betrogression 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 Avind-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-kamba as very large; the ear of A. aubryi, supposed to be of this species, was much smaller than that of " Johanna " ; AAhile 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 posterior 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 deATeloped in the Gorilla. " Johanna " possesses a very large lobule, measuring about 12 mm. in depth. The development of a Lobule in Gorillas and Chimpanzees. Total Lobule less than Less than More than Average. number. 10 mm. deep. 15 mm. deep. 15 mm. deep. Gorillas 25 4 16 5 10-4 mm. Chimpanzees. 14 9 4 1 3*4 m m. The average development of the lobule of the human ear is nearly 15 mm. Its meaning is unknown. |