208 The Phylogeny of the Ferearm Flexors 
portions of the mammalhan fascia may represent the portion of the am- 
phibian palmar aponeurosis which has disappeared in the reptilia I have 
studied. 
The phylogenetic history of the mammalian long flexors, which has 
been traced in the preceding pages, may be briefly stated as follows: In 
the primary condition the entire flexor mass of the forearm terminates 
at the wrist, a certain portion of it inserting into the bones of the forearm 
and carpus and the rest into a strong palmar aponeurosis. From the 
latter two sets of muscles take origin, (1) from its substance the flexores 
breves superficiales, and (2) from its deep surface the flexores breves 
medii. By the mode of origin of the first of these the palmar aponeu- 
rosis is divided distally into two layers, a more superficial one which is 
prolonged distally into strong tendons which insert into the bones of 
the terminal phalanges, and a deep one also prolonged into tendons which 
pass between the terminal steps of the flexores superficiales to unite with 
the superficial tendons. This is the amphibian stage. 
In the second or reptilian stage the portion of the superficial layer of 
the palmar aponeurosis which covers the flexores breves superficiales dis- 
appears and the action of the forearm flexors which insert into the apo- 
neurosis is distributed to the digits entirely through the tendons of the 
deep layer, which, together with the persisting terminal portions of the 
superficial tendons, may be recognized as the equivalent of the mamma- 
lian profundus tendons. The portions of the two layers of the forearm 
flexors which act on the aponeurosis fuse more or less completely, the 
flexores breves superficiales retain their amphibian relations, while the 
flexores medii divide into two layers, the more superficial of which repre- 
sents the lumbrical muscles of the mammalia. 
In the last or mammalian stage the flexores breves superficiales become 
transformed more or less completely into the tendons of the flexor sub- 
limis, and as the scale is ascended, a gradually increasing amount of the 
superficial portion of the flexor communis separates to become continu- 
ous with these tendons, until, in man, the entire condylar portion of the 
muscle, except so much as is represented by the palmaris longus, is taken 
up into the flexor sublimis. 
In the cases of the first and fifth digits some departures from the 
processes outlined above occur, but these may be more conveniently dis- 
cussed in connection with the history of the other hand muscles in a 
later paper. 
The results recorded above as to the relations of the sublimis tendons 
to the forearm muscles agree in general with those arrivel at by Eisler, 
but I have succeeded, I believe, in tracing with greater exactness the 
processes by which the final arrangement has been acquired. Lisler has 
