BONES OF THE HETACAEPUS AND PHALANGES. 



147 



Fig. 158.* 

 Bases. 



an. 



Front. 



whilst the thumb (i) has but two, its middle phalanx being de- 

 ficient, but they are strong- 

 er than those of the fin- 

 gers. 



[ 277. The PHALANGES 

 consist of base (fig. 159) 

 (1), body (2), and head 

 (3) ; they taper from the 

 base, or upper part of the 

 head, the intermediate part 

 or body being rounded be- 

 hind, and flat before, with 

 two projectinglateral edges 

 for giving attachment to 

 the sheaths of the ten- 

 dons. 



[ 278. In reviewing the 

 structure of the upper ex- 

 tremity, we have seen that 

 it consists of a series of 

 levers joined together, and diminishing progressively in length. 

 Thus, the arm is longer 

 than the fore-arm ; the lat- 

 ter is longer than the 

 and each joint 



hand ; 

 of the 



er than the one which it 

 succeeds. By this admi- 

 rable arrangement the nu- 

 merous joints in the hand 

 permit that useful instru- 

 ment to vary its motions in a 

 thousand different ways, to 

 adapt it to the various bo- 

 dies itis designed to handle, 

 grasp, and touch; whilst the 

 long levers formed by the 

 arm and fore-arm allow the hand to be rapidly changed to a con- 

 siderable distance in all directions. It is principally by the 

 movements of the humerus upon the scapula, that the direction 

 of the limb is given ; the flexion and extension of the fore-arm 



L2 



Fig. 159. 



Front. 



fingers is short- 



n 



in 



