DISCUSSION 197 



light on the reason for this. It is probably due chiefly to 

 a greater amount of freedom of movement between the bones 

 of the tarsus, and an adaptational arrangement of the 

 ligaments, the whole facilitated by the form of the articular 

 surfaces of the lower leg and the astragalus. 



The muscles flexing the foot, corresponding, it will be re- 

 called, to the extensors of the hand, are but three in number 

 and weak. The extensors, however, although but four, are 

 exceedingly powerful. The pedal extremity, being of fair 

 proportions for a generahzed mammal, constitutes a decided 

 aid during rapid locomotion, especially as an accessory to 

 the somewhat flexed lower leg. The structure of the gastroc- 

 nemii as well as the size of the entire Achillean muscle 

 mass composed of these two, the plantaris and soleus, 

 operating upon the extension of the calcaneum, constitute 

 an exceedingly powerful group for extension of the foot. 

 Pronation of the foot, by means of the peronei, is strong, 

 enabling this member to recover smartly after supination. 

 The two movements act antagonistically to preserve a 

 proper balance. 



As in the hand, the flexors of the toes, are strong, while 

 the extensors are much weaker. The extensor digitorum 

 longus is the only general extensor of the digits, and the 

 chief function of this seems to be as a flexor of the foot, for 

 when this work is performed, the force applied to extend the 

 toes is so slight that it is more than overcome by the flexors, 

 which in this position of the digits are mechanically tensed. 



The toes may be considered as having moderate grasping 

 power. As the foot is well supplied with small muscles, and 

 the hallux can be opposed to as great an angle as 90 degrees, 

 the animal can make good use of these members in negotiat- 

 ing slender twigs or performing other similar work. The 

 chief function of these muscles, however, is undoubtedly to 

 increase the strength of the foot as a whole and bind the 

 separate bones into a single unit. 



