Comparative Myology of the Chimpanzee. 371 



low the socket or centre of motion. Bat in the Quadru- 

 mana, and in most of the lower animals, the ischia are 

 lengthened and spread out, since the legs do not swing 

 behind them ; the Glutcei maximi arise chielly from the 

 tuberosities, and are inserted generally much lower on the 

 femur than in man, their increased length enabling them 

 to contract through a longer space, and they are thus pow- 

 erful retractors of the whole limb to a certain extent, 

 though not so as to bring it into line with the trunk, how- 

 ever strong they may be. In man the external surface of 

 the short, broad ilium looks outward like the acetabulum, 

 and the fibres of the Ghitceus medius converge from their 

 broad origin to the great trochanter ; the entire arrangement 

 being such that the muscle acts to prevent the body from 

 sinking to one side when supported by the opposite leg, 

 and also, from the great breadth of its origin to assist the 

 Glutceus maximvs and Psoas in preserving the balance 

 forward and backward, which also is required in ordinary 

 progression. But in the ape the external surface of the 

 ilium looks upward or backward, while the acetabulum 

 still looks outward as in man, thus at right angles with 

 that surface ; the ilia are long and narrow, so that the 

 fibres of the Glutcetis medius run nearly parallel to each 

 other, and the muscle is inserted at the end, not, as in 

 man, down the outer side of the trochanter, upon which in 

 the flexed state of the femur the muscle acts as upon the 

 short arm of a lever of which the leg is the long arm ; just 

 as in man when the femur is flexed, though to more ad- 

 vantage, on account of its attachment to the tip of the 

 trochanter. It also tends to rotate the limb inward, which, 

 when simple extension is required, is counteracted by the 

 simultaneous contraction of the Glutceus maximus, which 

 rotates in the opposite direction. It appears, then, that 

 the peculiar attitude of the ape is not connected with the 

 size alone of the Glutcei^ but that since he was not de- 



