498 THE MUSCULATURE 



Nerve-supply. — A branch from the medial plantar (or first plantar digital) nerve divides over 

 the plantar surface of the muscle and gives a twig to each belly near the middle third. Rarely 

 the lateral belly may receive a branch from the lateral plantar nerve. 



Relations. — The abductor hallucis covers it medially; the tendon of the flexor hallucis 

 longus passes between its two heads. Branches of the medial plantar vessels and nerve lie 

 on its superficial surface. 



The adductor hallucis (fig. 421). — The oblique head. — Origin. — From (1) the tuberosity 

 of the cuboid and the sheath over the tendon of the peroneus longus muscle; (2) the plantar 

 calcaneo-cuboid hgament; (3) the third cuneiform; (4) the bases of the second and third meta- 

 tarsals and (5) a fibrous arch which extends from the plantar calcaneo-cuboid ligament to the 

 interosseous fascia. 



Structure and insertion. — From short tendon-slips the fibre-bundles pass forward to form a 

 thick, fusiform belly which is attached in a bipenniform manner to a flat tendon. The tendon 

 begins about the middle of the plantar surface of the muscle and is inserted in common with that 

 of the flexor brevis into the lateral side of the plantar surface of the base of the first phalanx, 

 and by a slip into the aponeurosis of the long extensor muscle on the back of the big toe. 



Nerve-supply. — A branch from the deep ramus of the lateral plantar nerve enters the middle 

 third of the lateral border of the muscle on its deep surface. 



The transverse head arises from the joint-capsules of the third, fourth, and fifth metatarso- 

 phalangeal joints and from the transverse capitular ligaments. 



Structure and insertion. — Of the three fasciculi, that to the little toe lies nearest the heel, 

 that to the middle toe the most distally. The fibre-bundles take a nearly parallel coui-se to be 

 attached to tendon-slips which are fused into a common tendon that splits and passes on each 

 side of the tendon of the oblique head and is inserted into the sheath of the tendon of the long 

 flexor of the great toe (Leboucq). 



Nerve-supply. — A branch from the deep ramus of the lateral plantar nerve enters the middle 

 third of the deep surface of the muscle. 



Relations. — The adductor haUucis is crossed superficially by the tendons of the flexor 

 digitorum longus and by the lumbrical muscles. On its deep surface lie the interosseous muscles, 

 and the deep plantar vessels and nerves. 



Action. — The actions of the muscles of this group are indicated by the names of the individ- 

 ual muscles. The abductor and the oblique head of the adductor are also flexors of the first 

 phalanx. All the muscles of the group aid in extending the second phalanx. The transverse 

 head of the adductor serves to draw together the heads of the metatarsals after they have been 

 separated by the weight of the body during the tread. 



Variations. — The extent of fusion of the abductor and adductor with the two heads of the 

 short flexor varies considerably. The abductor may receive an accessory fasciculus from the 

 medial border of the foot. Either the adductor or the flexor brevis may send a tendon to the 

 base of the first phalanx or to the short flexor tendon of the second toe. The adductor shows 

 frequent variations in relation to its metatarsal attachments, owing to the fact that originally 

 a fasciculus from the body of the second (and third) metatarsal was probably normally present 

 and the transverse head was more developed (Leboucq). The opponens hallucis is a fasciculus 

 occasionally found which extends from the short flexor or the medial intermuscular septum to 

 the body of the first metatarsal. This muscle is normal in some monkeys. An adductor digiti 

 secundi has been seen to arise from various sources and become attached to the lateral side of 

 the plantar surface of the base of the first phalanx of the second toe. This muscle may be fused 

 with the oblique adductor. A corresponding muscle is found normally in some apes, and in 

 some of the lower animals there is a special adductor for each toe. 



d. Intrinsic Muscles of the Little Toe (figs. 419-421) 



In this group belong three muscles, an abductor, a flexor and an opponens. 

 The largest of these, the abductor digiti quinti (fig. 419), extends superficially over 

 the lateral margin of the foot from the lateral side of the tuber calcanei to the 

 base of the little toe. The flexor digiti quinti brevis (fig. 421) is a small, flat 

 muscle which lies on the plantar surface of the fifth metatarsal. The opponens 

 is a small muscle lying lateral to this. The two, which are often fused, arise from 

 the cuboid. The flexor brevis is inserted into the plantar side of the base of the 

 first phalanx of the little toe. The opponens is inserted into the lateral surface 

 of the metatarsal. The abductor corresponds with the a])ductor of the little 

 finger. The opponens and flexor bnnns correspond probably with the deep 

 part of the opponens of the little finger. I'lu; nerve supply is from the lateral 

 plantar nerve. 



The abductor digiti quinti (fig. 419). — Origin. — From (1) the lateral process of the tuber 

 calcanei and the lateral and plantar surface of tlie body of t he bone in front of tliis; (2) the lateral 

 intermuscular Hoj)tuni; Ci) the cl(!ep .surface of the lateral ])lantar fascia, including the fibrous 

 band extending from tin; calcancnis to the lateral si(l(^ of the base of the fifth metatarsal bone. 



Structure. — The fihre-bundles run obliquely to a flat tendon of insertion. This begins within 

 the muscle near tin; calcaneo-cuboid joint, soon emerges on the medial side of the deep surface, 

 and becomes free near the metatarso-phalangeal joint. Considerable individual variation in 

 structure is found. 



Insertion. — On the lateral surface of the first i)halanx of the little toe and the metatarso- 

 phalangeal capsule. Often a slip is sent to the extensor tendon. While usually the muscle 



