70 ANATOMY OF VERTEBRATES. 



In the toes of the fore-foot the last phalanx is retracted on the 

 ulnar side of the second phalanx. The principal elastic ligament 

 arises from the outer side and distal end of the second phalanx, 

 and is inserted into the upper angle of the last phalanx : a second 

 arises from the outer side and proximal end of the second phalanx, 

 and passes obliquely to be inserted at the inner side of the base 

 of the last phalanx : a third arises from the inner side and 

 proximal end of the second phalanx, and is inserted at the same 

 point as the preceding. The tendon of the 'flexor profundus 

 36 perforans' is the antagonist of these 



ligaments. The toes of the hind-foot 

 are retracted in a diiferent direction, 

 viz. directly upon, and not by the side 

 of, the second phalanx ; and the elastic 

 ligaments are differently disposed. They 

 are two in number, arise from the sides 

 of the second phalanx, and converge to 

 Elastic ligaments of Lion-s ciaw. ^ i nse rted at the superior angle of the 

 last phalanx. In fig. 36, a is the pair of elastic ligaments ; b, 

 the tendon which pulls out and works the claw; c, inelastic 

 ligament continued from the c extensor ' tendon, which is mainly 

 inserted into the second phalanx. 1 



The main purport of the modifications of the motory system in 

 Quadrumana is to make them climbers. By the developement 

 and direction of the hallux the hind-foot is converted into a 

 hand, with unusual power of prehension, especially in the Gorilla ; 

 the joint of this hand is so modified as to give it a free motion 

 excentric to the axis of the leg, whereby its outer edge is applied 

 to the ground ; the whole hind-limb is shortened, disproportion- 

 ately so in the best climbers (vol. ii. fig. 180), in which also the 

 hind-limb may be unfettered, for its acts of manipulation, by the 

 absence of the ' ligamentum teres ' of the hip-joint (Pithecus). 

 The length of the iliac bones relates to elongation of the muscles 

 for rotating the hind-limb and hand more quickly and through 

 greater spaces. Correlatively, the scapular arch approximates 

 to the condition of the pelvic one by the extension of complete 

 clavicles to the manubrium, and the head of the humerus is re- 

 ceived into a deeper and more secure socket than in Bimana. 

 This is well exemplified in the long-armed Gibbons, which enjoy 

 the peculiar mode of locomotion called ' brachiation.' The body 

 is set into pendulous vibration by the action and reaction of the 



1 The dissections of the Lion's foot showing the above-described modifications of 

 the elastic ligaments are Nos. 287a and 288a, Physiol. Series, vol. i. xx. 



