THE ASCENT OF MAN. 449 



The limbs, being orgaus of support and locomotion, show great varia- 

 tions in the zoological series, and the hand of man has long been looked 

 upon as especially significant of his high position in the animal king- 

 dom, one of the chief distinctions between him and the nearest brutes. 

 To a certain extent this is correct. No other creature possesses so highly 

 complex and effective an organ for grasping and adjusting objects, and 

 it is pre-eminently this that has made man a tool-nsing animal. On 

 comparing a human hand with that of the anthropoid apes it may be 

 seen that this efficiency is produced in two ways : first, by increasing 

 the mobility and variety of action of the thumb and fingers; second, by 

 reducing the muscles used mainly to assist prolonged grasp, they being 

 no longer uecessary to an organ that is intended for delicate work, 

 and requires constant re-adjustment. Thus some elements are added 

 and some taken away. Now according to the theory I have enunciated, 

 the latest elements ought to show signs of their recent origin, to be 

 somewhat im[)erfectly differentiated and liable to return to their primi- 

 tive state, while those going out of active use ought to be vestigial, not 

 equal in size or force to muscular organs generally, very liable to varia- 

 tion or disappearance. This is what actually occurs. 



Among the new elements is a special flexor muscle for the thumb, 

 arising high up on the forearm. A very slight examination shows 

 that this muscle has been split off" from the fibers of the deep fiexor 

 that bends the terminal joints of the fingers. lu most apes the two 

 form a single muscle, and in man the thumb flexor verj^ often shows 

 unmistakable evidence of such origin. In about 10 per cent, of 

 persons, part of its fibers pass over to and become blended with the 

 parent muscle. Not infrequently I have seen the two entirely united, 

 returning absolutely to their primitive condition. The deep and super- 

 ficial flexors of the fingers show signs of a similar relationship, as they 

 frequently blend more or less, tending to revert to the ty])e shown in 

 most lower animals. Indeed, if we go back to embryonic life we find 

 all the muscles of the anterior part of the fore-arm united in what is 

 termed tha pronato flexor mass, recialling the original condition of mus- 

 culature in the earliest aninuils possessing limbs. 



lu the category of disappearing muscles comes the palmarus longus 

 a muscle of the forearm which in many animals is an important aid in 

 climbing and grasi)ing. It takes its origin from the up[)er arm and 

 passes to the hand, where it expands into a large sheet of thick mem- 

 brane called the pabnar fascia, which splits into several slips passing to 

 each finger. The pull of the muscle acts upon all the Angers together, 

 keeping them bent without indei)en<lence of action. Now in man the 

 lingers have each two separate flexor tendons that can act to a certain 

 extent independently. To insure their independence they are at the 

 wrist enclosed in a remarkable tubular conduit or subway for?ne(l by 

 soldering the palmar fascia to the wrist-bones. This at once <lestroys 

 any effective action of the palmaris longus on the fingers and it becomes 

 H. Mis. 129 29 



