Comparative Myology of the Chimpanzee. 357 



long and generally powerfully prehensile tail, all being 

 very agile climbers ; and the Cebidac, Sakis, and others 

 whose tail is not prehensile, and who go often upon all- 

 fours. So much do the Anthropoids resemble ourselves 

 in external form and in their attitudes, as we see them in 

 captivity or represented in books, and so nearly also does 

 their internal structure correspond with our own, that we 

 are very apt to overlook the radical distinction in their 

 mode of locomotion, and to believe that in this as in other 

 respects they form the physical transition between the lower 

 animals and man. We walk upright upon the earth, and our 

 whole frame is perfectly balanced in that position ; we are 

 supported from below by comparatively narrow pedestals; 

 our whole weight is in direct opposition to the erect posi- 

 tion, and, as soon as we declined from it, would force us 

 to the earth but for the preponderance in the back and 

 legs, of the extensor over the flexor muscles. The position 

 of the ape in nature is just the reverse : he hangs and 

 moves about among the trees by means of his long arms, 

 being thus sustained, not from below, but from above ; 

 and his weight would soon bring him to the earth but for 

 the immense power of the Jlexor muscles in the arms. In 

 our arms, and in the legs of the ape, the two systems of 

 muscles are more nearly equal. Our legs are solely for 

 locomotion, our arms solely for prehension, and both pre- 

 sent the perfection of structure which would naturally 

 attend so high a degree of specialization of function ; but 

 both the upper and lower limbs of the ape may be employed 

 as organs of either support or prehension, and we therefore 

 remark in them a corresponding want of complete adap- 

 tation to either of these functions ; yet these so diverse mo- 

 tions of man and apes are performed by almost identical 

 muscles, while in the bird, which, like man, walks upon two 

 legs, with a very characteristic motion of the anterior ex- 

 tremities, the muscles are with great difficulty homologized 



