DEVELOPMENT OF THE POWER OF GRASP 21 



the palm (flexors), and others which can straighten them 

 out again (extensors). It is these finger muscles which 

 now become so important. We have noticed that some 

 of the less jDerfect tree-climbers run with great skill about 

 the branches, and that others climb rather than run, 

 but they obtain a grip by the specialized use of nails or 

 claws. It is a characteristic of the pioneer tree-climbers 

 we are picturing that they begin to grasp by the flexion 

 of their fingers, and obtain their grip, not by claws or 

 foot-pads or nails, but by an actual approximation of 

 the hand and the fingers to the objects up which they 

 desire to climb. 



The power to grasp with the hand and fingers seems 

 such a very simple accomplishment that it is difficult to 

 realize how such an apparently trivial beginning can have 

 produced the tremendous changes that follow in its 

 train. In essence its beginning depends upon the pre- 

 servation of a primitive second segment of the fore-limb, 

 for this has permitted the animal in its endeavours at 

 climbing to place the palmar surface of its hand and 

 fingers flat against the next hold for which it reaches out. 

 The mobility of the second segment already allows of 

 an adjustment of the hand to the object encountered. 

 Next, the hand by virtue of its flexor muscles makes the 

 adjustment more complete. In this way we may imagine 

 the flngers are closed over smaller branches, and the 

 animal begins to grasp. Although the picture is entirely 

 fanciful, we may iniagine that the higher the animal 

 climbs (the more perfectly arboreal it becomes), the 

 smaller the branches encountered, and so the more per- 

 fect the adjustment of the finger grasp. This picture, 

 although it may be dismissed as thoroughly outside the 

 precise demands of science, is nevertheless a useful one, 

 since in dealing with the modifications of such a primitive 

 fore-limb it is perfectly true to say that the more thor- 

 oughly an animal becomes an arboreal creature, the more 

 perfect becomes its hand grasp. The animal now reaches 



