614 MUSCULAR SYSTEM 



then passes the pad and is inserted like that of the second toe on 

 the base of its own second and third phalanges. 



In conformity with the separate position of the hallux, the 

 mass of deep flexors is divided into two principal portions, each 

 becoming a strong tendon which passes through or posteriorly over 

 the metatarsal pad and tubercle, then along the metatarsal groove 

 for insertion in various ways on the plantar face of the last or two 

 last phalanges, having in its course perforated the more super- 

 ficial tendons. It is convenient to distinguish these two portions, 

 the one as m. flexor perforans, the other as m. hallucis longus. 



M. flexor perforans s. profundus, arising from the greater part of 

 the hind face of the fibula and tibia, and rarely also from the outer 

 femoral condyle, runs covered by all the other flexors straight to 

 the intertarsal joint, which it passes more deeply than any of the 

 rest, entering between the pad and the tibio-tarsus, piercing the 

 former and immediately after the metatarsal tubercle as well. In 

 most Birds its tendon divides just above the distal end of the meta- 

 tarse, sending a slip to each front toe. 



M. flexor hallucis longus, regarded as the posterior portion of the 

 whole mass mentioned above, arises mostly from the intercondylar 

 space, with its belly resting upon that of the preceding, but slightly 

 towards the outer or fibular side, and its tendon in most cases 

 accompanying that of the preceding, there to pass either through 

 the tarsal pad and hypotarsus, resting in this case on the posterior 

 surface of the other tendon, or lying a little towards its outer side, 

 superficially over the pad and tubercle, after which both run down 

 the metatarsal groove, that of the present resting on the plantar 

 and fibular side of the other. About half-way down the middle of 

 the metatarse the tendon of the m. flex, hallucis splits into two 

 parts, one, continued as the so-called vinculum to the front tendon, 

 the other, which is generally the weaker, to be inserted on the last 

 phalanx of the hallux. It is obvious that the tendon of the m. 

 flex, hallucis, after passing over the outer part of the ankle, must 

 cross the deeper tendon obliquely to reach the hallux, a crossing 

 which is correlated with its reversed position, and is really double, 

 because the m. flex, hallucis arising more inwardly than the m. flex, 

 perforans, and thus crossing it laterally, crosses it once above 

 the joint and then again upon the metatarse, since its tendon 

 goes to the hallux. It is also clear that, owing to the vinculum, 

 contraction of the m. flex, hallucis bends not only the hallux but the 

 other toes as well, while the m. flex, perforans acts on the front toes 

 only. This m. flex, hallucis is therefore, properly speaking, a m. 

 flexor communis, and the so-called m. flex, perforans is the anterior 

 portion of the whole mass of deep flexors, a view which is justified 

 by the fact that the m. flex, hallucis is present regardless of the 

 absence of the hallux. 



