196 The Phylogeny of the Forearm Flexors 
dylo-ulnaris (C.U.), lying beneath the medial head of the flexor carpi 
ulnaris (F. C. U’) and the palmaris longus (PL) and ventral to the 
ulnaris (U1), the condylo-radialis (CR) lying to the radial side of the 
palmaris and the condylo-ulnaris, while between it and the radialis is 
the slender centralis (C), which corresponds to the “ slender little spindle 
of muscle, quite distinct from the rest,” described by Coues (1872), 
whose identification of it with the flexor longus pollicis is manifestly 
erroneous. ‘Tracing the various portions down the arm, it is found that 
Fig. 5. Transverse section through the forearm of the Opossum. ai, anterior 
interosseus nerve; C, centralis; CR, condylo-radialis; CU, condylo-ulnaris; F. C. 
R., flexor carpi radialis; F. C. U.! and F. C. U.*, lateral and medial portions of the 
flexor carpi ulnaris; m, median nerve; PL, palmaris longus; R, radius; Ra, radialis; 
U, ulna; w~, ulnar nerve; UL, ulnaris. The shaded areas represent the flexor subli- 
mis digitorum. 
the condylo-uwlnaris decreases in size rather rapidly, its fibres passing into 
a flat tendon which lies on the surface of the muscle in contact with the 
ulnaris. A portion of the muscle, represented. approximately by the por- 
tion which is shaded in Fig. 5, may, however, be traced onward to the 
wrist where it passes into ‘a tendon lying to the ulnar side of and super- 
ficial to the large tendon which is formed by the fusion of the main 
condylo-ulnar tendon with the other four portions of the flexor com- 
munis. Later the superficial condylo-ulnar tendon divides into three 
