OSSEOUS SYSTEM OF MAMMALIA. 97 



Of all the Mammalia, in Man alone the posterior limbs are the sole 

 organs of progression ; and in him they are exclusively appropriated to 

 this purpose. Walking erect, his posterior limbs have to bear the whole 

 of the body's weight, and to maintain its due equilibrium. Let him run, 

 or leap, or walk, whether slowly or rapidly, these organs sustain him, pre- 

 serve him steadily and firmly in his usual attitude, and obey him, as far 

 as the power with which they are endowed will admit. It need hardly be 

 observed that the feet are incapable of grasping, being destitute of an 

 opposable thumb, and that they are plantigrade ; that is, so constructed, 

 as to allow the sole, from the heel to the toes, to be fairly applied to the 

 surface of the ground ; while, at the same time, the arched form of the 

 instep contributes, with the action of the large muscles of the calf (the 

 tendons of which are inserted into the heel), to secure an elastic step, 

 and a free, yet firm progression. Allusion has been before made to the 

 volume of muscles on the leg (forming, what is termed, the calf), as essen- 

 tial to the elastic step of Man. No other animal possesses a well-formed 

 and decided calf, because no other animal walks as he does : at each step, 

 while one foot is in the act of advancing, and just before it is brought to 

 the ground, the heel of the other foot is raised by the action of these 

 muscles, so as to throw the weight of the body momentarily on the 

 toes. Hence the strain on the tendo Achillis, in walking ; a strain in- 

 creased while running, leaping, or dancing ; or on dropping from any 

 height upon the toes (a mode dictated By instinct, in order to break the 

 concussion) ; and there are not infrequent instances, where a sudden 

 and violent effort has occasioned the rupture of this tendon, into which 

 the muscles of the calf converge. The action of these muscles is that of 

 flexors of the ankle-joint : they draw the foot backward, and, in this 

 position, retain it with great power, and more or less permanently, as the 

 occasion may be. If we stand on tip-toe for a length of time, we begin 

 to feel the muscles of the calf aching with fatigue ; and the same sen- 

 sation, succeeded by stiffness, results after a toilsome walk ; after skating, 

 dancing, and similar exercises. 



Not only do the lower limbs of Man differ from those of all other 

 animals in the possession of the calf, but, also, in general configuration ; 

 in the proportions of the parts composing them ; and in the superiority, 

 as to bulk, which they exhibit, compared with that of the arms. With the 

 exception of the Kangaroo, the Gerboa, and a few other rodents, no 

 other animals exhibit anything like this disparity, because their four 

 limbs are all equally organs of locomotion ; all equally sustain the body's 

 weight. In such as use the fore limbs for striking, seizing, digging, &c., 

 as well as for the purpose of locomotion, the anterior limbs even greatly 

 preponderate in volume, in many instances. Such is the case in the Ape 

 tribe, the nearest to Man in external configuration ; for example, in the 



