ANTHROPOID APES AND MAN 



451 



some adjustment to tree life, as in the opposable character of the great 

 toe, are more fitted for locomotion on the ground. 



452. Erect Position. — In an animal going upon all fours the vertebral 

 column forms an arch and the greatest degree of flexibility is at the base 

 of the neck and at the base of the tail. With the assumption of the 

 erect position there come changes which are shown somewhat by the 

 semi-erect apes but which are exhibited completely only by man. One 

 of these changes is the appearance of curvatures in the spine needful 



lateral fissure 

 Cerebrum 



CenfrcfJ sulcus 



Fig. 347. — Human brain from the side. From a preserved specimen. The roots of the 

 cranial nerves are indicated by roman numerals. 



in the balancing of the erect body. Thus the human spine comes to 

 have a backward curvature in the thoracic and sacral regions and a 

 forward curvature in the neck and lumbar regions. A second change 

 is in the increasing development of the bodies of the vertebrae at the 

 lower end of the trunk where the weight is transmitted to the legs. 

 With the complete emancipation of the forelimbs from any part in locomo- 

 tion and their specialization for other purposes, the pectoral girdle 

 becomes lightened and less firmly connected to the axis of the body. 

 On the other hand the pelvis remains strongly developed, is closely 

 attached at right angles to the body axis, and is broadened for the support 

 of the viscera. The leg bones also become straighter and the great toe 

 ceases to be opposable. The foot becomes arched, which is an adaptation 



