THE VERTEBRATE BODY 143 



The skull and vertebral column form the main skeletal axis 

 from which is suspended the appendicular skeleton, or bony 

 framework of the paired appendages (fins or limbs) and their 

 supporting structures (girdles). This is relatively simple in the 

 anterior (pectoral) and posterior (pelvic) paired fins of Fishes, 

 which merely act as paddles; but when these are modified into 

 paired limbs for progression on land, the mechanical problems 

 involve the development of complex limb skeletons to support the 

 body, and to act as levers for the limb muscles to move in locomo- 

 tion. In response to this need an elaborate series of bones is de- 

 veloped which, in all cases, however, may be referred to a common 

 plan, known as the pentadactyl limb in allusion to the five digits 

 (fingers and toes) in which it usually terminates. The limbs are 

 attached directly or indirectly to the vertebral column by groups 

 of bones which form respectively the pectoral and pelvic gir- 

 dles. (Figs. 102-104, 227, 228.) 



E. The Human Body 



Considering specifically the human body, we find that its out- 

 standing characters are largely the result of Man's erect posture. 

 True it is that the body is not perfectly adapted to its upright 

 position, but this is more than compensated for by the complete 

 division of labor between the upper and lower limbs that liberated 

 the former from contributing to locomotion and gave the oppor- 

 tunity for the pentadactyl plan to attain its highest development 

 in the human hand. With its completely opposable thumb, the 

 hand is directly or indirectly responsible for more of Man's unique 

 characters than one usually realizes. It is an efficient grasping 

 organ — a battery of tools that makes possible the use of artificial 

 tools which, in a way, may be regarded as accessory organs, de- 

 vised by the brain and appropriated or discarded at will. 



But the hand is also a delicate 'sense organ' since touch is "the 

 great confirmatory sense" underlying many of our sensory ex- 

 periences with the world about us. "Tactile fingers are continually 

 learning." Indeed, it is largely upon a basis of conscious and sub- 

 conscious tactile sensations that much of the superstructure of 

 the higher mental processes is reared. It seems clear that the erect 

 posture and the facile hand have contributed in no small way to 

 the supremacy of the brain and so to Man's outstanding position 

 above the beasts. (Figs. 105, 125.) 



