106 THE RELATIONS OF MAN 



but one ; and its metatarsal is far less moveably articu- 

 lated with the tarsus, than the metacarpal of the thumb 

 with the carpus. But a far more important distinction 

 lies in the fact that, instead of four more tarsal bones there 

 are only three ; and that these three are not arranged side 

 by side, or in one row. One of them, the os calcis or heel 

 bone (ca), lies externally, and sends back the large project- 

 ing heel ; another, the 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 sepa- 

 rated from the three inner tarsal bones of the row next 

 the metatarsus by a bone called the scaphoid (so). 



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 metacarpals and metatarsals, with their respective 

 digits, are compared together. 



The same two classes of differences become obvious 

 when the muscles of the hand are compared with those of 

 the foot. 



Three principal sets of muscles, called " flexors," bend 

 the fingers and thumb, as in clenching the fist, and three 

 sets, — the extensors — extend them, as in straightening the 

 fingers. These muscles are all " long muscles ; " that is 

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

 to the bones of the arm, is, at the other end, continued 

 into tendons, or rounded cords, which pass into the hand, 

 and are ultimately fixed to the bones whfch are to be 

 moved. Thus, when the fingers 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, connected with their ends, 



