46 



The rii^ylogeny of the Crural Flexors 



The amphibian plantaris profundus I is represented in Scincus by 

 two distinct muscles. The first of these, which may be termed simply 

 the plantaris profundus I (Figs. 4 and 5, Pp^), arises from the posterior 

 surface of the lower part of the fibula and is directed obliquely downward 

 and inward. It passes over into a flat tendon which lies beneath (ante- 

 rior to) the tibial border of the tendon of the plantaris profundus III-II, 

 and, indeed, is to a certain extent connected to the deep surface of the 

 sesamoid bone developed in that tendon. It separates from it again, 

 however, and is continued on over the large tarsal bone of the first row 

 (astragalo-calcaneus) and is inserted into the two inner bones of the 

 second row of the tarsus. This is the muscle which has very generally 

 been recognized as the tibialis posticus. 



The second muscle, which may be 

 termed the plantaris profundus I acces- 

 sorius (Fig. 5, Pp^a). arises from the 

 plantar surface of the fibular portion of 

 the large astragalo-calcaneous {Fac) 

 and is directed obliquely inward and 

 downward, passing posteriorly to the 

 lower part of the plantaris profundus I 

 (Pp^), to be inserted into the sesamoid 

 bone (s) developed in the tendon of 

 the plantaris profundus III-II. 



Finally, there is a well developed 

 interosseus muscle (Figs. 3 and 4, 7) 

 which passes across from the fibula to 

 the tibia, filling up the interval between 

 the two bones through almost its entire 

 length. In the upper part of the mus- 

 cle (Fig. 3) the fibers have an almost 

 vertical direction, but, as it is traced 

 downwards, the lower fibers, which pass 

 over to the tibia anterior to the higher ones, become more and more 

 oblique, until finally in the lower part of the crus (Fig. 4) all the fibers 

 •c.re exceedingly oblique, some almost transverse, and the vertical upper 

 fibers are seen as a small bundle (I^) lying upon the posterior surface 

 of the tibia, completely isolated from the oblique ones. The higher 

 vertical fibers are inserted into the outer (fibular) and posterior sur- 

 faces of the lower half of the tibia, while the lower oblique fibers pass 

 to its anterior and inner surfaces, wrapping around the lower end of 

 the bone. 



Fig. 5.— Transverse section through 

 the ankle of Scincus sp. a, superficial 

 portion of plantar aponeurosis; o/, 

 deep portion of plantar aponeurosis; 

 /, ramus superticialis fibularis; FAC, 

 flbulare-astrag-alo-calcaneus ; fc, fib- 

 ular cutaneous nerve ; p, ramus pro- 

 fundus; Ppl, plantaris profundus I; 

 Ppla, plantaris profundus I accesso- 

 rius ; s, sesamoid bone in deep portion 

 of plantar aponeurosis ; T, tibia. 



