J. Playfair McMurrich 



49 



3, p) on its posterior surface and is continued downward through that 

 muscle, to which it gives branches, and, emerging from it at the ankle, 

 (Fig. 6, p) it sends twigs to the plantaris profundus I and to the plan- 

 taris profundus I accessorius and is then continued into the foot as 

 the internal plantar nerve. 



Accepting the interpretation of the nerves of the amphibian crus 

 given above and comparing on the basis of their nerve supply the muscles 

 of the amphibian and lacertilian crus the following result is obtained. 



Nerve. 

 R. superf. medialis, 



R. superf. fibularis, 

 R. profundus, 



Amphibia. 

 Plantaris superf. medialis, 



Plantaris superf. lateralis, 



Plantaris profundus III, minor, 

 Plantaris profundus III, 

 Plantaris profundus II, 



Fibulo-tarsalis, 



j Plantaris profundus I, 

 I Interosseus, 



Lacertilia. 

 Plantaris superf. medialis. 

 Plantaris superf. tenuis. 

 Plantaris superf. lateralis. 

 Plantaris superf. accessorius. 



Plantaris profundus III-II. 



r Plantaris profundus I. 



\ Plantaris profundus I, accessorius. 



Interosseus. 



It is clear from this that a close comparison based both upon the 

 topographical relations and the nerve supply can be made between the 

 crural flexors of the amphibia and those of the lacertilia, there being, 

 however, in the latter a greater amount of differentiation of the original 

 layers. It is interesting to note that just as in the lacertilian arm no 

 representative of the ulno-carpalis could be distinguished, so too in the 

 crus there appears to be no representative of the amphibian fibulo-tarsalis. 



III. The Crural Flexors in the Mammalia. 



In considering the crural flexors of the mammalia it will be con- 

 venient to depart from the method of description and nomenclature 

 followed in the preceding pages, and to consider the various muscles as 

 independent structures, employing the terms usually assigned to them 

 in mammalian myology. In other words, the primary layers will be 

 temporarily neglected, the reference of the individual muscles to them 

 being considered later on. 



A considerable amount of confusion seems to have existed with 

 reference to the soleus and gastrocnemius. Thus, the latter muscle has 

 been described as possessing but a single head in certain forms, the 

 lateral head being described as the soleus; in others the soleus is sup- 

 posed to be included in the lateral head of the gastrocnemius; and in 

 one case even, the medial head of the latter muscle has been termed 



