40 The riiylogeny of the Crural Flexors 



ing independently at dill'erent levels. And, furthermore, a more import- 

 ant difference exists in the origin of a branch to the plantaris profundus 

 III from the ramus profundus above its point of fusion with the ramus 

 superficialis. This might seem to vitiate any direct homology between 

 the ramus plantaris profundus and the ramus palmaris profundus, but, 

 on the other hand, it may be a part of the same lack of differentiation of 

 the plantar nerves which is evidenced in the retention of extensor fibers 

 in the ramus plantaris profundus. In Cryptobranchus, according to 

 Humphry, 72, both the ramus profundus and the ramus superficialis 

 send branches to the plantaris profundus III, and in Menopoma, to judge 

 from Eisler's figures, 95, the two stems separate only at the upper border 

 of the plantaris profundus II, from which it may be presumed that the 

 branches to the plantaris profundus III are given off from the common 

 stem above the bifurcation. Whether the high or the low bifurcation be 

 the more primitive condition, it is difficult to say, but it is at least plausi- 

 ble to suppose that the fusion of the two trunks in Amblystoma presents 

 opportunities for the transference of fibers destined for the plantaris 

 profundus III (and possibly II) from the ramus profundus to the ramus 

 superficialis, since, apparently, the fibers which form the lower cross 

 connection between the two stems are destined for the supply of the 

 plantaris profundus II. 



However that may be, it seems clear that in the plantar nerves there 

 is less definiteness in the differentiation of the nerve fibers into special 

 trunks than occurs in the palmar nerves, a fact which is shown by the 

 inclusion of prgeaxial fibers in the same trunk with postaxial ones 

 throughout the entire length of the crus and by the inclusion of fibers 

 destined for superficial muscles in the same trunk with others for the 

 deep muscles. 



Tabulating the nerve supply of the plantar muscles according to the 

 origin of the fibers from the two main stems the following arrangement 

 If obtained : — 



Plantaris superficialis medialis, ] 



Plantaris superficialis lateralis, | 



Plantaris profundus III (in part), \- Ramus superficialis. 



Fibulo-tarsalis, j 



Plantaris profundus II, J 



Plantaris profundus III (in part), ^ 



Plantaris profundus I, I Ramus profundus. 



Interosseus, j 



but, if the interpretation of the plantar nerves given above on the basis 

 of a comparison with the arm nerve be accepted, the tabulation will be as 

 follows : — 



