THE FATE OF THE HIND-LIMBS 40 



arboreal life, the hind-limb never becomes a mere stable 

 prop ; it becomes the principal support of the body weight, 

 but it is a support which is bearing a body undergoing 

 endless changes of poise. Moreover, it is discharging this 

 function among the branches of a tree; the foot is not 

 resting on the ground, it is placed in apposition with a 

 branch. The sole of the foot becomes applied to the 

 branch of a tree, in the same manner as does the palm 

 of the hand. The mobility of the second segment of the 

 lower limb becomes limited and restricted to definite 

 lines, but it does not become lost; the simple condition 

 of the foot becomes retained even if not so completely 

 as in the fore-limb. The power of grasp of the foot is 

 developed, though not to the degree of perfection which 

 is seen in the hand. We may imagine the evolutionary 

 story to have been carried out somewhat on these lines. 

 The animal pauses in its attempts to climb, it reaches 

 for a new hold with its hands, and so trusts to its legs 

 for its support. Later, the power to grasp becomes 

 more perfectly developed in the hand, and when it has 

 secured a new hold it can grasp and suspend the body 

 weight while the foot reaches farther ahead for a new 

 foothold; a degree of mobility of the second segment of 

 the leg is thus retained, and a degree of development of 

 grasp with the foot is thus developed. From the attain- 

 ment of this stage, two divergent developments are 

 possible. The hind-leg may develop a degree of mobility 

 and of grasp equal, or almost equal, to that of the hand, 

 a condition which fits the animal for the time-honoured 

 distinction as quadrumanous or four-handed. The foot 

 may become, equally with the hand, a grasping and 

 suspending organ; or the hand and forearm may be 

 specialized as the mobile grasping-suspending organ, and 

 the leg and foot as the supporting — still somewhat mobile 

 and somewhat grasping — organ. It is the grasping- 

 supporting and not the grasping-suspending leg that has, 



from this common point of divergence, led to better things. 



•1 



