THE HUMAN FRAME. 371 



instruments of progression by their greater length and mus- 

 cularity, compared with the generality of quadrupeds. The 

 only exceptions to this rule occur in those mammalia which 

 are constructed expressly for leaping, such as the Kanguroo 

 and Jerboa^ where, however, the hind legs are employed 

 almost solely for that mode of progression. The Quadru- 

 mana, which come nearer to the human form than any of 

 the other tribes, have the lower limbs comparatively weak. 

 In almost all other quadrupeds the disproportion is still 

 greater, the thigh being short, and almost concealed by the 

 muscles of the trunk, and the remainder of the limb being 

 slender, and not surrounded by any considerable mass of 

 muscles. 



The articular surfaces of the knee joint are broader, and 

 admit of greater extent of motion in man than in quadru- 

 peds: hence the leg can be brought into the same line with 

 the thigh, and form with it a straight and firm column of 

 support to the trunk; and the long neck of the thigh bone 

 allows of more complete rotation. The widely spread basin 

 of the pelvis effectually sustains the weight of the digestive 

 organs, and they rest more particularly upon the broad ex- 

 pansion of the iliac bones: in quadrupeds, these bones, havino- 

 no such weight to support, are much narrower. 



The base on which the whole body is supported in the 

 erect position is constituted by the toes, and by the heel, 

 the bone of which projects backwards at right angles to the 

 leg. Between these points the sole of the foot has a conca- 

 vity in two directions, the one longitudinal, the other trans- 

 verse, constituting a double arch. This construction, be- 

 sides "conferring strength and elasticity, provides room for 

 the convenient passage of the tendons of the toes, which 

 proceed downwards from the larger muscles of the leg, and 



dent purpose of brlng-Ing- the fore limbs nearer to each other, that they 

 might more effectually support the anterior part of the trunk. In Man, on 

 the contrary, the thorax is flattened anteriorly, and extends more in widtli 

 than in depth} thus throwing- out the shoulders, and allowing an extensive 

 range of motion to the arms. 



