POSTERIOR PART OF LOWER EXTREMITY. 393 



the under surface of the os calcis ; the long plantar ligament. Insertion, the 

 upper surface and outer oblique border of the flexor longus digitorum. Demon- 

 strate carefully on your dissection the specific double origin and double insertion 

 of this muscle. To do this, hold the heel firmly and extend the toes vigorously. 

 Nerve-supply, the external plantar, a branch of the posterior tibial. 



The lumbrical muscles are four in number. They arise in connection with the 

 tendons of the flexor longus digitorum, as follows : The first from the great-toe 

 side of the first tendon, beginning at the point where this tendon leaves the main 

 tendon of the muscle. The other three arise from the adjacent tendon, as seen in 

 figure 270. Insertion, into the inner border of the expanded tendons of the ex- 

 tensor communis digitorum. The nerve-supply is from the external plantar for 

 the two outer ; the internal plantar for the two inner. Acting with the interossei, 

 these muscles flex the metatarso-phalangeal articulation and extend the first and 

 second interphalangeal joints. Note, then, the homology, both in nerve-supply 

 and function, of these muscles and the lumbricales manus. 



The intimate association of the accessorius and lumbricales pedis with the 

 flexor longus pollicis and flexor longus digitorum justifies some authors in classi- 

 fying these latter also in the second group. For details of these muscles, which 

 are not here considered as belonging to the second, the reader is referred to 

 page 389. 



Name tJic muscles of the third layer of tJu\ sole of tJic foot, giving origin, inser- 

 tion, function, and nerve-supply. 



The Flexor Brevis Hallucis. Origin, from the under surface of the cuboid 

 bone ; the long plantar ligaments ; the expansion of the tibialis posticus in the 

 middle of the sole of the foot. Insertion, base of the first phalanx of the great 

 toe, both on the inner and outer borders. (Fig. 268.) The tendon of the flexor 

 longus hallucis passes between the two parts of the muscle, playing over a pulley 

 formed by the two sesamoid bones developed in the tendon of flexor brevis hal- 

 lucis. (Fig. 274.) This muscle flexes and slightly adducts the first phalanx. 



The Adductor Hallucis (Fig. 274). Origin, the sheath of the peroneus longus 

 formed by the long plantar ligament ; the under surface of the second, third, and 

 fourth metatarsals. Insertion, into the outer part of the base of the first phalanx 

 of the great toe. Nerve-supply, the external plantar. 



The Transversus Pedis (Fig. 274). Origin, the deep transverse metatarsal 

 ligaments and the plantar ligaments of the three outer metatarso-phalangeal 

 articulations. Insertion, into the base of the first phalanx of great toe on the 

 outer side. Nerve-supply, the external plantar. Action, to adduct the great toe. 



The Flexor Brevis Minimi Digiti. Origin, base of fifth metatarsal bone, under 

 surface (Fig. 268); sheath of peroneus longus. (Fig. 274.) Insertion, into the 

 under surface of base of first phalanx of the little toe. Action, to flex the little 

 toe. Nerve-supply, the external plantar. 



The interossei have been fully considered. The student is urged to study 

 carefully the action of these muscles, both separately and in conjunction with the 

 lumbricales. 



26 



