200 The Phylogeny of the Forearm Flexors 
doubt. There is no question but that, in the arm I studied, the entire 
mass of the condylo-radialis passed into the flexor sublimis, and the ulnar 
head of the radialis, 7.e. the 
longus pollicis, is readily account- 
ed for by the fact that that por- 
tion not infrequently takes its 
origin from the ulna as well as 
from the radius. 
The various portions of the sub- 
limis possess an interesting rela- 
tion to the digits. The tendons 
for the two ulnar fingers come 
from the condylo-ulnaris; that 
for the medius is formed entirely 
from the condylo-radialis and in 
the arm lies to the radial side of 
the tendon for the index, crossing 
obliquely over that tendon upon 
its palmar surface at the wrist; 
the index tendon is formed 
mainly from the centralis, though 
I could not be certain that it did 
Fiag.8. Transverse section through the fore- C = 
arm of a human embryo of 4.5cm. Lettering not also include some portions of 
in Fig. 5. , 
a a the condylo-wlnaris. 
The history of the sublimis, then, seems to be as follows: In the 
mammalian prototypes the arrangement of the forearm flexors was 
somewhat as is now found in the monotremes, there being a single flexor 
mass without any marked differentiation of a superficial and a deep 
portion. The single tendon formed from this mass divided at the wrist 
into a superficial set of sublimis tendons and a deep set representing 
the profundus, but the muscle mass of the forearm showed no such sepa- 
ration. Its first differentiation consisted in the separation of a pal- 
maris longus, which became attached to the minimal sublimis tendon as 
well as to the palmar fascia, and a portion of the condylo-ulnaris sepa- 
rated and became continuous with the other three sublimis tendons. 
Later the entire condylo-ulnaris was brought into connection with the 
sublimis and the portion of the palmaris which joined the ulnar tendon 
separated from that muscle and became incorporated in the condylo- 
ulnaris. In higher forms the centralis also united with the sublimis 
tendons as well as a portion of the condylo-radialis and, finally, in the 
anthropoids and in man, all the superficial or condylar portions of the 
