202 The Phylogeny of the Forearm Ilexors 
lV. THe EXTENSION OF THE LONG FLEXORS INTO THE HAND. 
We come now to the concluding chapter in the history of the flexors 
of the forearm. It has been shown that they are primarily confined to 
the forearm, acting on the digits only by the intervention of the palmar 
aponeurosis and the palmar muscles which arise from it, and it remains 
to be seen how the direct connection with the digits which they possess 
in the mammalia has been brought about. 
Fig. 9. Fie. 10. 
Fig. 9. Transverse section through the third and fourth metacarpals of Ambly- 
stoma tigrinum. F. B. P., flexor brevis digitorum profundus; F. B. M., flexor brevis 
medius; F. B.S., flexor brevis superficialis; I. M., intermeta-carpalis; M!! and M!V, 
third and fourth metacarpals; p. a. s., and p. a. d., superficial and deep layers of the 
palmar aponeurosis. 
Fie. 10. Transverse section through the second and third digits of Amblystoma 
tigrinum. ¥F. P., and F. P./, flexor brevis digitorum profundus; F. M., median por- 
tion of flexor brevis medius; F. M.’, portion of flexor brevis medius which unites 
with the flexor profundus; F.S., median portion of flexor brevis superficialis; F. 8.7, 
portions of the flexor superficialis which unites with the flexor profundus; /, lumbri- 
calis; i. e., lateral portion of the flexor medius; pt, profundus tendon; st, superficial 
tendon. 
To do this it is necessary to return to the amphibia and consider the 
relations of the palmar and forearm muscles to the palmar aponeurosis. 
