J. Playfair McMurrich 37 



in Amblystoma, a derivative of the plantaris profundus III and may be 

 termed the plantaris profundus III minor. 



The fibulo-tarsalis (FT) arises from the posterior surface of the upper 

 part of the fibula and extends vertically down the crus, lying immedi- 

 ately behind the fibula, to be inserted into a strong tendinous band which 

 extends transversely across the sole of the foot at about the level of the 

 distal row of tarsal bones. This muscle is the fibulo-plantaris of Eisler, 

 the deep common flexor of the phalanges of Perrin, the fibulae-metatarsi 

 et digiti I-V of Hoffmann and the flexor profundus digitorum of 

 Humphry. 



The plantaris profundus II (Pp^^) also arises from the posterior 

 surface of the fibula and takes an oblique direction downwards and 

 tibially to be inserted into the deeper (dorsal) surface of the plantar 

 aponeurosis. It is the plantains profundus I of Eisler, the internal 

 flexor of the digits of Perrin and the femoro-flbulge metatarsi I-III of 

 Hoffmann. 



The plantaris profundus I (Pp^) arises from almost the whole length 

 of the fibula and from the tarsus and is directed downward and tibially 

 to be inserted into the lower end of the tibia, into the tibiale and the 

 tarsale I; I did not find any insertion into the plantar aponeurosis in 

 Amblystoma. This is the muscle described by Perrin as the direct 

 rotator of the foot, and is apparently represented in Menopoma, accord- 

 ing to Eisler, by four more or less distinct muscles which have been 

 named the plantares profundi II and III, the fibulo-tibialis and the 

 fibulo-tarsalis. Humphry and Hoffmann have not recognized it as dis- 

 tinct from the plantaris profundus 11. 



Finally, the interosseus (I) is a strong band of muscle fibers which 

 extend almost directly across between the tibia and fibula, occupying 

 the position of the interosseous membrane of the higher mammalia. It 

 is the pronator tibiae of Humphry and the fibulae-tibialis of Hoffmann. 



In the study of the arm flexors much light was thrown upon their 

 phylogenetic modifications by their nerve supply and the same holds good 

 for the crural flexors. It must be remembered, however, that with the 

 modifications which the muscles undergo in the various groups, a modi- 

 fication of the nerve trunks also occurs, and in making use of the nerve 

 supply for the identification of muscle equivalents in the different groups, 

 these changes in the paths followed by the nerve fibers must be taken into 

 consideration. The final test in the identification of a motor nerve is its 

 end organ, the muscle; that is a definite quantity in the problem. But 

 the path by which a given nerve reaches its end organ is not necessarily 

 the same in all cases ; the nerve, as a rule, will seek the most direct route 



