84 THE HUMAN BODY. 



mobile than they usually are, so that the foot can to a 

 certain extent replace the hand; as has been illustrated in 

 the case of persons born without hands who have learned to 

 write and paint with their toes. 



Peculiarities of the Human Skeleton. These are largely 

 connected with the division of labor between the fore and 

 hind limbs referred to above, which is carried farther in 

 man than in any other creature. Even the highest apes 

 frequently use their fore limbs in locomotion and their 

 hind limbs in prehensioft, and we find accordingly that 

 anatomically they present less differentiation of hand and 

 foot. The other more important characteristics of the 

 human skeleton are correlated for the most part with the 

 maintenance of the erect posture, which is more complete 

 and habitual in man than in the animals most closely allied 

 to him anatomically. These peculiarities, however, only 

 appear fully in the adult. In the infant the head is pro- 

 portionately larger, which gives the centre of gravity of the 

 Body a comparatively very high position and renders the 

 maintenance of the erect posture difficult and insecure.[ 

 The curves of the vertebral column are nearly absent, and 

 the posterior limbs are relatively very short. In all these 

 points the infant approaches more closely than the adult 

 to the ape. The subsequent great relative length of the 

 posterior limbs, which grow disproportionately fast in 

 childhood as compared with the anterior, makes progression 

 on them more rapid by giving a longer stride and at the 

 same time makes it almost impossible to go on "all fours" 

 except by crawling on the hands and knees. In other Pri- 

 mates this disproportion between the anterior and posterior 

 limbs does not occur to nearly the same extent. 

 l~ In man the skull is nearly balanced on the top of the 

 vertebral column, the occipital condyles which articulate 

 with the atlas being about its middle (Fig. 27*), so that but 

 little effort is needed to keep the hotid erect. 'In four-foot- 

 ed beasts, on the contrary, the skull is carried on the front 

 end of the horizontal vertebral column and needs special 

 ligaments to sustain it. For instance, in the ox and sheep 

 there is a great elastic cord running from the cervical ver- 



*P. 75. 



