THE FOOT. 



281 



This gradual reduction of the digits is accompanied by a simplifica- 

 tion and alteration of the carpal and tarsal, metacarpa] and i aria tar- 

 sal bones; the metacarpals (metatarsals) of the rudimentary or absent 

 digits are reduced to styliform bones or are entirely absent, while 

 the two middle metacarpals (metatarsals) (3 and 4) are often united 

 to form a strong and long tubular bone. The small carpal and 

 tarsal bones which are employed in the formation of the foot-joint, 

 and serve essentially to diminish the shock produced by the move- 

 ments of the limbs when used in locomotion, are arranged usually in 

 two, sometimes in three rows; in the tarsus, two bones the astra- 

 and calcaneum are usually much larger than the rest. The 



r; 



'J 3 



FIG. 670. Skeleton of hand of a, oning ; I, dog ; c, pig ; d, ox ; e, tapir ;/, horse (I, c, d, 

 after Gegeubaur). R, radius; U, ulna; A, scaphoid; , semi-lunar; C, iriquetrum 

 (cuneiform); D, trapezium; E, trapezoid ; F, capitatum (magnum); <?, hamatum (uiici- 

 form) ; P, pisiform ; C, centrale carpi ; M, metacarpus. 



digits of the anterior foot may be called fingers after the analogy of 

 the human hand. The anterior foot becomes a hand when the inner 

 finger or thumb is opposable. The great toe of the posterior foot is 

 also sometimes opposable, but the foot does not on this account 

 become a hand, but only a prehensile foot (Apes) ; for the hand is 

 characterised by the special arrangement of the carpal bones and 

 muscles. According to the manner in which the foot rests on the 

 ground in movement, animals are distinguished as plantigrades, 

 digitigrades and unguligrades. In the last case the number of digits 

 and metacarpals (and metatarsals) is reduced, and the limb is much 

 elongated by the transformation of the metacarpal (metatarsal) bone 

 into a long tubular bone. 



