THE PHYLOGENY OF THE PLANTAR MUSCULATURE. 
BY 
J. PLAYFAIR McMURRICH. 
From the Anatomical Laboratory of the University of Michigan. 
WitH 9 TExT FIGURES. 
In three papers which have appeared in this JourNAt I have given the 
results of a comparative study of the flexor muscles of the antibrachium, 
hand and crus, and have shown that in each of these parts there is an 
arrangement of the musculature in definite layers, which can be identified 
in the amphibia, reptilia and mammalia. And, further, it was shown that 
there is a close correspondence in the arrangement of the musculature of 
the antibrachium and crus in the lower forms. There remain to be deter- 
mined the existence of an arrangement in primary layers in the plantar 
musculature and the correspondence of these layers with those occurring 
in the palm. In the present paper I shall consider especially the question 
of the primary layers of the plantar musculature and their differentiation. 
The material which has served for this study consisted of series of 
transverse sections of the same forms that were employed in my study of 
the crural flexors, 04, except that, through the courtesy of Dr. M. J. 
Greenman, Director of the Wistar Institute of Anatomy, I have been able 
to add to the mammalian series a representative of the Insectivora, Scap- 
hanus sp.?, which, unfortunately, however, proved to be of only subordi- 
nate value for my purpose, owing to the extensive transformation of the 
plantar musculature into tendinous structures. I have also had oppor- 
tunity for studying the plantar muscles of Jguana tuberculata, through 
the courtesy of my colleague, Dr. J. E. Reighard. 
I. THE PLanTar MUSCLES OF THE URODELE AMPHIBIA. 
The plantar muscles of Amblystoma are arranged in four primary lay- 
ers, which correspond, layer for layer, with those occurring in the palm. 
In a transverse section through the foot a little distal to the bases of the: 
metatarsal bones, the arrangement represented in Fig. 1 is seen. Super- 
ficially, immediately beneath the integument, is the strong plantar 
aponeurosis (pa), beneath which lies a continuous layer of muscle tissue, 
AMERICAN JOURNAL OF ANATOMY.—VOL. VI. 
32 
