236 HISTORY OF THE HUMAN BODY 



minal phalanges, as that function has been usurped by the 

 other muscle. 



Upon the ventral side a more intimate connection between 

 the tendons of the palmar aponeurosis and the associated 

 muscles gives rise to the system of long flexors, as found in the 

 higher vertebrates. In the arm, where this history has been 

 most completely followed, the palmaris muscles, superficial and 

 deep, uniting with the palmar fascia and its long tendons, form 

 the two long flexors characteristic of mammals, flexor digit- 

 orum sublimis and profundus. In the monotremes the bellies 

 form a common mass, flexor communis digitorum, although 

 with double tendons to the separate digits, a deep tendon which 

 inserts on the terminal phalanx and a superficial tendon which 

 forks. The two resulting parts insert upon the edges of the 

 penultimate phalanx, and allow the deep tendons to pass 

 through between them. A later differentiation of the belly 

 divides it into a flexor profundus, continued into the deep ten- 

 don, and a flexor sublimis, continued into the superficial tendon. 

 The most superficial of the fibers separate into the somewhat 

 inconstant "palmaris longus." The flexor pollicis longus of 

 man belongs with the profundus. 



The tendons of the short superficial flexors of amphibians 

 become mainly employed in the formation of the profundus 

 tendons, while the bellies degenerate, but those associated with 

 digits I and V develop in the mammalian hand and foot into 

 special muscles connected with those digits, such as the abduc- 

 tors of pollex and minimus, the opponentes of the same, and 

 the flexor brevis minimi digiti. The short, deep flexors of the 

 amphibians, flexores breves profundi, become the mammalian 

 lumbricales; and the still deeper set of abductors and adduc- 

 tors, together with the intermetacarpales, become the two sets 

 of interossei, palm-ares and dorsales, the latter arising upon the 

 ventral aspect and coming through to the dorsal side during 

 development. 



The four muscles which in Necturus lie along the ulnar and 

 radial sides of the antebrachium on both dorsal and palmar 



