228 MOTION AND COORDINATION 



6. The Leg and Foot Groups. These correspond in form 

 and arrangement to the bones of the arm and hand. Since, 

 however, the leg and foot are used for purposes different 

 from those of the arm and hand, certain differences in 

 structure are to be found. The patella, or kneepan, has no 

 corresponding bone in the arm ; and the carpus, or ankle, 

 which corresponds to the wrist, contains seven instead of 

 eight bones. The bones of the foot and toes are the same 

 in number as those of the hand and fingers, but they differ 

 greatly in size and form and have less freedom of motion. 

 The femur, which gives form to the thigh, is the longest 

 bone of the body. The tibia, or shin bone, and the fibula, 

 the slender bone by its side, give form to the lower part of 

 the leg (Fig. 102). 



The legs are mechanical devices (walking machines) for 

 moving the body from place to place. The feet serve both 

 as supports for the body and as levers for pushing the 

 body forward. By their attachment to the legs they may 

 be placed in all necessary positions for supporting and 

 moving the body. 



The different bone groups are shown in Fig. 97 and 

 named in Table IV. 



Adaptation to Special Needs. When any single bone is studied in 

 its relation to the other members of the group to which it belongs or 

 with particular reference to its purpose in the body, its adaptation to 

 some special place or use is at once apparent. Each bone serves some 

 special purpose, and to this purpose it is adapted by its form and struc- 

 ture. Long bones, like the humerus and femur, are suited to giving 

 strength, form, and stiffness to certain parts, while irregular bones, like 

 the vertebrae and the pelvic bones, are fitted for supporting and pro- 

 tecting organs. Others, like the wrist and ear bones, make possible a 

 peculiar kind of motion, and still others, like the ribs, are adapted to 

 more than one purpose. The vast differences in shape, size, structure, 

 and surface among the various bones are but the conditions that adapt 

 them to particular forms of service in the body. 



