184 The Phylogeny of the Forearm Flexors 
The R. profundus (Fig. 2, rp) bends mesially and dorsally, curving 
around the radius, and comes to he dorsal to the pronator quadratus, 
in which position it descends the arm. It supples the pronator qua- 
dratus and also the pronator accessorius and the flexor carpi radialis, 
and at the lower border of the quadratus it passes ventrally so as to 
lie upon the ventral surface of the carpus (Fig. 3, rp), giving off 
a branch to the oblique portion of the palmaris communis. 
The R. superficialis divides, as in the amphibia, into a R. medialis 
(Fig. 2, rsm) and a R. ulnaris (rsu). The latter passes obliquely 
across the arm between the superficial and deep layers of the palmaris 
communis, reaching the ulna at the lower edge of the insertion of 
the epitrochleo-anconeus, which muscle it supples, also sending twigs 
to the lateral head of the flexor carpi ulnaris. It then continues down 
the arm, lying to the ulnar side of the deep portions of the palmaris 
communis and so passes into the manus. 
The R. medialis follows at first the course of the ulnaris until it 
reaches approximately the median line of the arm, when it gives off 
branches to the more median head of the flexor carpi ulnaris. arly in 
its course it gives a branch to the pronator radii teres. It passes down 
the arm between the superficial and deep portions of the palmaris com- 
munis, both of which it supplies and in which it is finally lost. 
Tabulating the muscles according to their nerve supply the arrange- 
ment is as follows: 
. Epitrochleo-anconeus 
) Stan 3 
Flexor carpi ulnaris (lateral head) ee supericah saa 
Palmaris communis (superficial portions) 
Palmaris communis (deep portions II & IIT) 
Flexor carpi ulnaris (median head) 
Pronator radii teres | 
R. superficialis medialis. 
Palmaris communis (oblique portion) 
Pronator quadratus 
Pronator accessorius 
R. profundus. 
Flexor carpi radialis 
We are now in a position to make a comparison of the individual 
amphibian and reptilian muscles. On the ulnar side the epitrochleo- 
anconeus has become more distinctly separated from the flexor carpi 
ulnaris in the reptilia, and with the latter muscle a portion of the pal- 
maris superficialis has associated itself to form the medial head, while 
the rest of the palmaris superficialis, represented by the superficial por- 
tions of the palmaris communis, shows a tendency to divide into two 
portions. 
The palmares profundi II and III are represented by the deep por- 
