6-i 



The Phylogeny of the Crural Flexors 



of the paths followed by the nerve fibers which supply the flexor muscles 

 of the crus. Stated in general it consists of (1) a separation of the 

 fibers destined for the internal plantar region from the ramus profundus 

 and their assumption of a more superficial course, a process which occurs 

 also in the antibrachium ; (2) a breaking np of the ramus superficialis 

 medialis into a number of branches which arise independently; (3) the 

 union of the internal and external plantar nerves to form the posterior 

 tibial; and, finally, the association of some fibers of both the ramus 

 superficialis medialis and the ramus profundus with the posterior tibial. 



Taking the reptilian arrangement for a starting point, the rearrange- 

 ment as it is shown in the opossum, in the mammalia in general as repre- 

 sented by the cat and the mouse, and in man may be schematized thus: — 



Lacertilia. 



Ramus sujierf. jued- 

 ialis. 



Ramus superf. fibu- / 

 laris. \ 



Ramus profundus. < 



Opossuin. 



Branches to the super- 

 ticial musfles* 



External plantar. 

 Internal plantar 



Branches to the deep 

 muscles and perios- 

 teum. f 



Cat and Mouse. 



Branches to the super- 

 ficial muscles* 



Posterior Tibial 



Branches to the deep 

 muscles and iierios- 

 teuni.t 



Man. 



Branches to gastrocnemii, 

 soleus and iilantaris. 



Posterior Tibial. 



Branches to popliteus, 

 tibialis posticus and the 

 n. interosseus cruris. 



*By the superficial muscles are here meant the gastrocnemii, plantaris, soleus and flexor flbularis. 



t By the deep muscles are here meant the fiesor tibialis, tibialis posticus and pronator tibiie (popliteus). 



V. The Homologies of the Mammalian Crural Flexors. 



Having now described the arrangement of the muscles in the three 

 vertebrate groups selected for study and having also elucidated the 

 modifications presented by the primary nerve stems, we are in a position 

 to determine the homologies of the mammalian muscles with those of 

 the lower forms. A comparison of the lacertilian and amphibian muscles 

 has already been made and the comparison now to be drawn might be 

 principally with the lacertilia, were it not that it will be necessary in the 

 following pages to make frequent reference to the conclusions of Eisler, 

 95, who deduces the mammalian arrangement directly from the amphi- 

 bian, neglecting altogether the reptilian. It will be convenient to con- 

 sider the various muscles in succession and to take the arrangement seen 

 in man as a type. 



1. The gastrocnemius of man is formed by the union of two heads, 



