THE PHYLOGENY OF THE FOREARM FLEXORS. 
BY 
J. PLAYFAIR McMURRICH, Ph. D. 
From the Anatomical Laboratory of the University of Michigan. 
WirtH 13 TExt FIGURES. 
Notwithstanding the voluminous literature of descriptive myology, 
comparatively little has been accomplished toward the determination 
of the exact homologies of the hmb muscles throughout the vertebrate 
phylum. Something has been done in the way of elucidating a funda- 
mental plan for the mammalian muscles, especially through the efforts 
of Ruge, Cunningham, Windle, Leche and von Bardeleben, to mention 
only some of the more recent authors, but even with regard to this group 
there are still gaps to be filled out and the earlier stages in the phylogeny 
still require study, notwithstanding Hisler’s very important contribution 
to that side of the story. That author (1895) has made a careful study 
of the limb muscles of the urodelous amphibia, taking Menopoma as a 
type, and has attempted to reduce the mammalian condition to a modifi- 
cation of what obtains in that group. Having omitted to consider the 
reptilia, however, Eisler has missed some important points bearing on 
the question, and I propose in the following pages to give the results of 
observations made on both amphibia and reptilia and hope to demon- 
strate a detailed homology of the arm muscles in these groups and then 
to extend the homologies to the mammalian muscles. 
My attention was primarily directed to the subject through some 
study which I had made of the perforated flexors of the hand and foot. 
It has been a general custom to regard these muscles as equivalent and 
to assume that the primary condition, so far as mammalia are concerned, 
is represented in the arm and that there has been a secondary recession 
of the muscle into the foot in the lower limb (cf. Wiedersheim, 1893). 
On looking into the matter it seemed that the evidence which could be 
brought forward in support of such a theory was decidedly scant, and I 
determined to test it by a phylogenetic study, beginning with an attempt 
to trace the evolution of the flexor sublimis of the arm. ‘This muscle, 
as a distinct element, being, however, confined to the mammalia, it was 
evident that in order to obtain a correct appreciation of its significance 
