34 



The riiylogcny of the Crural Flexors 



a representative of the reptilia and the opossum {Didelpliys virginlana) ^ 

 the mouse, the cat and man as representatives of the mammalia. 



I. The Crural Flexors of the Urodelous Amphibia. 

 A transverse section through the upper part of the crus of Ambly- 

 stoma shows the arrangement of parts represented in (Fig. 1). Super- 

 ficially upon the posterior surface of the section is seen a strong, some- 

 what crescentic, muscular mass, which, employing a terminology con- 

 sistent with that used in the description of the antibrachial muscles, 



may be termed the plantaris super- 

 ficialis medialis (Psm) . It may be 

 remarked in passing that while the 

 terms used by Eisler, 95, in his 

 careful and suggestive paper on the 

 homology of the extremities are also 

 employed here, their application is 

 very different, since Eisler has failed 

 to recognize the muscle now referred 

 to as a distinct constituent of the 

 crural flexor mass, that muscle which 

 he terms the plantaris superficialis 

 lying beneath the muscle now under 

 consideration and forming what I 

 shall describe as the plantaris pro- 

 fundus III. 



In addition to this most superficial 

 muscle, there is upon the outer side 

 of the leg another muscle (Psl) 

 which must also be referred to the 

 superficial layer and which may be 

 termed the plantaris superficialis lateralis. 



Beneath the superficial layer formed by these two muscles lies a larger 



Fig. 1.— Transverse section throug-h the 

 upper part of the crus of Anihljistoma 

 tiorinum. F, fibula; /, ramus superticialis 

 flbularis; FT, tibulo-tarsalis; I, interos- 

 seus; m, ramus superticialis medialis; p, 

 ramus profundus ; Pp I-IIf, plantares pro- 

 fundi I-III ; PpiJJm, plantaris profundus 

 III minor; Psl, plantaris superticialis la- 

 teralis; P.sm, plantaris superticialis medi- 

 alis ; r, tibia. 



* As on a former occasion, I am indebted to my friend, Dr. C. F. W. McClure, 

 for the opossum material which was used, and I desire to express my apprecia- 

 tion of his courtesy in placing at my disposal material without which my 

 studies would necessarily have been very incomplete. 



To my assistant, Mr. F. S. Bachelder, I am greatly indebted for assistance 

 in the work, since he kindly undertook the preparation of all the serial sec- 

 tions that were required. He also studied with me the arrangement of the 

 muscles and nerves of the amphibian crus and so much of this paper as 

 treats of these structures is to be regarded as our joint work. 



