358 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



While the results of the erect position show that 

 man has been able to adapt his altered mode of pro- 

 gression to the mechanical conditions of an organisa- 

 tion, best suited for quadrupedal movement, it is to be 

 noted that (1) the space between the 

 thorax and the pelvis leads to. and is the 

 cause of, prolapse and other affections of 

 the uterus, and of hernia in both sexes ; 

 (2) the carotids which supply the most 

 important of organs, the brain, have to 

 carry their contents against the action of 

 gravity, and, for this reason, they are of 

 large size. Or, to put it in another way, 

 the erect position entails certain positive 

 disadvantages. 



In other members of various divisions 

 of Vertebrates, by far the most important 

 part in support or locomotion is often 

 undertaken by the hind limbs ; this is 

 especially well seen in hopping or jump- 

 ing forms, as, for example, the frog, 

 where the tarsal bones are greatly elon- 

 gated and the digits of considerable 

 length; in the jerboa, where the meta- 

 tarsals are very long ; or the kangaroo, 

 where the calcaneum (c) is very long, the 

 cuboid (CB) very strong, and the meta- 

 tarsal of the fourth digit greatly elon- 

 gated ; in other words, we have here a continuous 

 series of well-developed bones lying along one axis, 

 and affording a firm support (Fig. 153). 



When the extremities are used as seizing organs, 

 the pollex of the manus and the hallux of the pes are 

 qpposable on the other digits ; such an arrangement 

 obtains in the higher Primates, but in man, where the 

 foot has more of a supporting than of a prehensile 

 function, this power of opposition is lost in many races 



ig. 153. 

 RigM Pes 

 of Kanga- 

 roo. 



