J. Playfair McMurrieh 39 



the plantaris profundus III (Pp^^^) and below the fusion a branch 

 (Ex.) which passes downward and forward through a notch on the crest 

 of the tibia and is supplied to the muscle which has been termed the 

 tibialis anticus. The main stem then gives off a branch (7) to the 

 interosseus, and having in its downward course passed successively over 

 the upper border of the plantares profundi III-I, it passes over the upper 

 border of the interosseus and is continued downward on the extensor sur- 

 face of that muscle (Fig. 1, p). Before reaching the foot it gives off 

 a branch and then divides into two stems, one of which, together with 

 the branch, passes to the muscles upon the dorsum of the foot, while the 

 other passes backwards beneath the lower border of the interosseous 

 muscle, gives off a branch to the plantaris profundus I and continues 

 onward to be distributed to the plantar surface of the foot. 



In order to understand the significance of this arrangement of the 

 nerves it will be necessary to compare it with what occurs in the arm. 

 In this but a single nerve trunk, the brachialis longus inferior, enters the 

 flexor surface of the antibrachium and it divides into a ramus profundus 

 and a ramus superficialis. The former has a course almost identical 

 with that of the ramus profundus of the crus and supplies the pronator 

 quadratus and the palmaris profundus I, which have the same topo- 

 graphical relations as the interosseus and plantaris profundus I supplied 

 by the ramus plantaris profundus. The latter nerve, however, also con- 

 tains some extensor fibers which are lacking in the deep nerve of the 

 antibrachium, the separation of the prseaxial and postaxial fibers having 

 taken place higher in the arm than in the leg. 



The ramus superficialis of the antibrachium divides into two portions, 

 a ramus superficialis medialis and a ramus superficialis ulnaris, the 

 latter of which possesses relations similar to those of the ramus plantaris 

 superficialis after it has given off its branches to the plantares profundi 

 III and II. It would seem, therefore, that these branches may well be 

 regarded as equivalent, in part at all events, with the ramus superficialis 

 medialis of the arm, while the main stem below their origin may be 

 considered the equivalent of the ramus superficialis ulnaris and be termed 

 the ramus superficialis fihularis. 



But the ramus superficialis medialis of the arm supplies not only the 

 palmares profundi III and II, but also the palmaris superficialis. In 

 the leg the branches which are distributed to the muscles which I have 

 identified as forming the plantaris superficialis, are given off from the 

 ramus superficialis above the point of its fusion with the ramus pro- 

 fundus, so that a difference from the arrangement in the arm exists in 

 that there is no concrete ramus superficialis medialis, its branches aris- 



