192 The Phylogeny of the Forearm Flexors 
cles with those of an amphibian. His homologies may be stated briefly 
as follows: The superficial palmar of the amphibia is represented by 
the palmaris longus, having become very much reduced in size correl- 
atively with a marked increase in the size of the deep palmars. Of 
these the palmaris profundus II, gradually extending its origin proxi- 
mally and radially, becomes transformed into the flexores digitorum 
profundus and longus pollicis; the palmaris profundus III similarly 
migrates proximally upon the ulna and eventually, passing over the 
elbow joint, reaches the internal condyle of the humerus and becomes 
the flexor digitorum sublimis; while the profundus I is normally un- 
represented in the mammalian forearm, but occasionally appears as the 
anomalous radio-carpeus of Fano (the flexor carpi radials brevis seu 
profundus of Wood). 
It seems to me that these results are open to criticism along three 
general lines. In the first place the omission of all consideration of the 
reptilia has placed Eisler at a disadvantage in having no bridge over 
the enormous gap which undoubtedly exists between the urodelous am- 
phibia and the mammalia. Even if we accept an amphibian ancestry 
for the mammalia, it seems probable that the ancestors were much more 
reptilian in character than are any of the existing urodeles and, further- 
more, not only must the mammalian musculature be referred back to 
the amphibian but so must the reptilian. Accordingly we may expect 
to find in the reptilian muscles, if not direct evidence of the phylogeny 
of the mammalian conditions, at all events indications of the lines 
along which it proceeded and, it seems to me, this expectation has been 
fully borne out by the results described in the preceding pages. There 
is certainly much more general similarity in the arrangement of the 
reptilian and mammalian forearm musculature than in that of the 
amphibia and mammalia. 
In the second place Eisler has failed to take into consideration the 
evidence derived from the nerve supply of the amphibian musculature. 
It may not be possible as yet to institute a certain homology between the 
amphibian and mammalian forearm nerves, but I believe that I have 
shown a sufficient general equivalency to warrant the acceptance of the 
nerve supply as important corroborative evidence. The identification, 
therefore, of the palmaris profundus II with its nerve supply from the 
R. superficialis medialis with the mammalian flexor profundus supplied 
by fibres which represent the R. profundus, seems very doubtful, unless 
the evidence from other sources is more than ordinarily convincing, and 
that it is so has not, I believe, been demonstrated. 
Yhirdly, the homologies proposed by Eisler demand a very consider- 
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