122 MAN AND THE LOWER ANIMALS. n 



astragalus (as), rests on this by one face, and by 

 another, forms, with the bones of the leg, the 

 ankle joint; while a third face, directed forwards, 

 is separated from the three inner tarsal bones of 

 the row next the metatarsus by a bone called the 

 scaphoid (sc). 



Thus there is a fundamental difference in the 

 structure of the foot and the hand, observable 

 when the carpus and the tarsus are contrasted: 

 and there are differences of degree noticeable when 

 the proportions and the mobility of the metacar- 

 pals and metatarsals, with their respective digits, 

 are compared together. 



The same two classes of differences become 

 obvious when the muscles of the hand are com- 

 pared with those of the foot. 



Three principal sets of muscles, called " flex- 

 ors,' 7 bend the fingers and thumb, as in clench- 

 ing the fist, and three sets, — the extensors — ex- 

 tend them, as in straightening the fingers. These 

 muscles are all "long muscles"; that it to say, 

 the fleshy part of each, lying in and being fixed to 

 the bones of the arm, is, at the other end, con- 

 tinued into tendons, or rounded cords, which pass 

 into the hand, and are ultimately fixed to the 

 bones which are to be moved. Thus, when the fin- 

 gers are bent, the fleshy parts of the flexors of the 

 fingers, placed in the arm, contract, in virtue of 

 their peculiar endowment as muscles; and pulling 

 the tendinous cords, connecting with their ends, 



