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. haiiucis 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 vinculwm 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. flea. 
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 conmunis, 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. 
