206 The Phylogeny of the Forearm Flexors 
In the case of the fifth digit the conditions are slightly different, in 
that the superficial sheet of the flexor medius does not extend laterally 
beyond its radial border, and hence, when the division of the sheet into 
separate slips takes place, that for the minimus lies upon the radial side 
of its digit and does not divide into 
two terminal slips as do the others, 
but imserts entirely into the radial 
side of the arthrodial fibrocartilage. 
The arrangement of these muscle- 
shps is shown diagrammatically in 
Hieewli2: 
If now we proceed to compare 
these arrangements with those seen 
in the amphibia we arrive at the 
following conclusions. The  por- 
inn Bitie atmuneauient Ge the nat oncane tion of the superficial layer of the 
(l), in Liolepisma laterale. F. B. S., flexor Siac as 
brevis superficialis; ph, phalanx; pl, pro- amphibian palmar aponeurosls,, 
EES ee oer which covers the flexor brevis super- 
ficialis, has disappeared in the reptilia or is represented in the 
flexor, if one prefers to state it that way. The more proximal por- 
tions of the apeneurosis, however, are represented by the volar cartilage, 
and the strong tendons which are continued distally toward the fingers 
from the volar cartilage are, in their proximal portions, the representa- 
tives of the tendons formed from the deep layer of the amphibian 
aponeurosis.. Beyond the point of the bifurcation of the slips of the 
flexor superficialis these tendons in the amphibia fuse with the tendons 
Fic, 18. Diagram showing the mode of formation of the profundus tendon. F. 
B. S., flexor brevis superficialis; F. B. M., flexor brevis medius; P. A., palmar 
aponeurosis. The stippled portion of the aponeurosis disappears in the reptilia. 
from the superficial layer of the aponcurosis, and it is probable that in 
the reptilia the tendons from the same point are equivalent to those of 
the amphibia. The annexed diagram (Fig. 13) will give, I trust, a 
sufficiently clear idea of the arrangement in the two groups, the portion 
of the amphibian aponeurosis which has disappeared in the reptilia being 
indicated by the stippling. 
From the reptilian arrangement as interpreted above to the mamina- 
lian the passage is easy. The tendons which are continued distally from 
the volar cartilage to the digits clearly correspond to the mammalian 
