1905.] MR. R. I. POCOCK OX A HAIXAX GIBBOX. 179 



stand third in climbing, third in bipedal and first in quadi^npedal 

 powers. 



Since, therefore, the action of Monkeys, whether Cercopithecidse, 

 Cebidte, or Hapalidfe, and of Lemurs is essentially^ quadrupedal, 

 the fore and hind limbs being used to an approximately equal 

 extent, both in terrestrial and arboreal locomotion, it may be 

 inferred that the Chimpanzees have departed least in these 

 respects from the primitive Primate stock ; the Gorillas a little 

 more in the line of bipedal erection and, concomitantly, loss of 

 climbing power ; the Orangs still moi'e in the direction of loss 

 of terrestrial activity and increase of arboreal expertness ; the 

 Gibbons most of all in the line of bipedal activity, dexterity in 

 hand-climbing, and loss of cjuadrupedal power. 



This serial arrangement of the Apes is the exact opposite 

 of the one prevalent in text-books, where the order adopted is 

 based upon structure with Man placed first as the standard for 

 comparison. It suggests that for the origin of Gibbons we must 

 look not to forms resembling any known Oercopithecoid type, but 

 to forms which had already acquired the Simiine or Anthropo- 

 morphine characteristics and had either lost or never learnt the 

 method and skill in climbing found in the former group. They may 

 have started from a type somewhat on a level with the Chimpanzees 

 with respect to terrestrial and arboreal activity ; and to swing with 

 greater facility from tree to tree and to obviate the risk of injury 

 in case of a fall, it is highly probable that they have become 

 dwarfed in stature and grown lighter in build. Their muscularity 

 and length of arm, slightness of body and strength of leg, all factors 

 of importance in enabling them to traverse the jungle and, in 

 case of a miss or a breaking branch, to drop lightly to the ground 

 and run to the nearest tree for safety, were probably perfected 

 concomitantly. That Gibbons are able to drop with safety a 

 considerable distance is substantiated by the fact that Mr. de 

 St. Croix has seen his specimen come to the ground without 

 injury from a height of about 20 feet. When leaping to the 

 ground Gibbons swiftly draw up the knees as the feet touch, 

 exactly as a man does under similar circumstances, to break the 

 shock. 



Another interesting feature connected with the habits of the 

 Anthropoid Apes is the size of their ears. I have already suggested 

 that the difference in size between the ears of the Orang and 

 those of the Chimpanzee may be connected with the difierence of 

 habits of the two animals. The Orang lives a moi-e arboreal and 

 therefore a safer life than the Chimpanzee, which requires quick 

 hearing to enable it to escape to the trees when feeding on the 

 ground"*. Gibbons also, which have relatively large ears, need 

 auditory acuteness for the same purpose as Chimpanzees. This 

 explanation, however, is not complete and appears at first sight to 

 be contradicted by the case of the Gorillas, which have small ears 



* 'Nature,' Oct. lltli, p. 585 (1900). 



12* 



