180 The Phylogeny of the Forearm Flexors 
dus ITI, arising from the radial side of the lower part of the wna and 
inserting into the dorsal surface of the palmar aponeurosis toward its 
radial edge; and, finally, most radial of all, is the palmaris profundus 1 
(P. P. 1), which arises from the lower part of the ulna and also from 
the carpus and may be traced distally and radially to an insertion into 
the aponeurosis and the base of metacarpale II. As has been already 
stated the distinction between portions I and II is not always quite 
evident and there is also a close relationship between I and the muscle 
of the third layer, the pronator quadratus (P.Q.), both being supplied 
Fic. 1. Transverse section through the lower half of the forearm of Amblystoma 
tigrinum. F.C. R., flexor carpi radialis; F.C. U., flexor carpi ulnaris; PP/-PP///, 
first to third portions of palmaris profundus; PQ, pronator quadratus; PS, palmaris 
superficialis; R, radius; rp, ramus profundus; rsm, ramus superficialis medialis; 
rsu, ramus superticialis ulnaris; U, ulna; UC, ulno-carpalis. 
by the same nerve; portion II has, however, a different nerve supply, 
receiving branches from the same stem which supplies portion III. 
The relations of these muscles as seen in sections may be perceived 
from Fig. 1, which represents a transverse section through the lower 
half of the antibrachium of Amblystoma tigrinum. 
Turning now to the lacertilia one finds a condition which seems at 
first sight far removed from that obtaining in the amphibia. There is 
a greater amount of longitudinal division of the muscle layers and a 
