48 



The Pliylogeny of tlie Crura] Flexors 



One of them (F) passes down into the crns upon the fibular side of 

 the plantaris supcrficialis lateralis and gives off a couple of large cuta- 

 neous branches (C) which are distributed to the fibular side of the leg, 

 one of them (Figs. 4 and 5, fc) passing far down the crus in the groove 

 between the fibular border of the plantaris supcr- 

 ficialis lateralis and the peroneus. The main stem 

 in its downward course gradually verges medially, 

 so that it comes to lie beneath the plantaris supcr- 

 ficialis lateralis (Figs, 4 and 5, /) and, indeed, be- 

 comes partly enclosed in the substance of that 

 muscle. It appears to give off no branches in the 

 crus, nor could any twig to the plantaris supcr- 

 ficialis lateralis be found arising from it. At the 

 ankle it passes into the foot towards its fibular 

 border, and is then recognizable as the external 

 plantar nerve. 



This nerve is evidently that referred to by Ga- 

 dow, 82, as stem III, and, notwithstanding its 

 somewhat different course in its upper part, is ap- 

 parently equivalent in part to the ramus super- 

 ficialis fihularis of Ambly stoma, but, unlike it, is 

 quite distinct from the branches which represent 

 the ramus supcrficialis medialis, a difference which 

 may well be correlated with the absence of an 

 anastomosis between the flexor stems in the lacer- 

 tilia. 



The other main stem, before leaving the thigh, 

 divides into two trunks (Fig. 6, m. and rp.), both 

 of Avhich pass downwards to the tibial side of the 

 plantaris superficialis lateralis. The more posterior 

 trunk (m), the stem I of Gadow, may from its dis- 

 tribution be termed the ramus superficialis medialis. 

 Shortly after entering the crus it divides into 

 several branches which are entirely confined to the crus and supply all 

 the portions of the plantaris superficialis, as well as the plantaris pro- 

 fundus III-II. 



The deeper branch (rp), the stem II of Gadow, may be termed the 

 ramus profundus. It passes towards the tibia and divides into two 

 branches, the posterior of which (Fig. 6, c; Figs. 3 and 4, pc) is cuta- 

 neous and is distributed to the skin over the tibial surface of the crus. 

 The deeper branch enters the substance of the the m. interosseus (Fig. 



Fig. 6.— Diagram of the 

 crural nerves of Scincus 

 sp. A, nerve to extensor 

 surface ; c, cutaneous 

 nerves ; EP, external 

 plantar ; 2*', ramus super- 

 ficialis ttbularis; I,branch 

 to interosseous; IP, in- 

 ternal plantar ; m, ramus 

 superficialis medialis ; 

 Mp, common trunk of 

 ramus superficialis med- 

 ialis and ramus pro- 

 fundus; Ppi, branch to 

 plantaris profundus I ; 

 Ppla, branch to plantaris 

 profundus I accessorius ; 

 PpII-III, branch to plan- 

 taris profundus II-lII ; 

 Psa, branch to plantaris 

 superficialis accessorius ; 

 Psl, branch to plantaris 

 superficialis lateralis ; 

 Psm, branch to plantaris 

 superficialis medialis ; 

 Pst, branch to plantaris 

 superficialis tenuis ; rp, 

 ramus profundus. 



