FLEXOR ACCESSORIUS. DIGITORUM PEDIS 381 



nerve, by lilanients which enter the back part of the deep surface of the muscle 

 near its inner border. 



Action. — (1) To abduct i\w lirst phahxnx of the httle toe from the middle Hne; 

 (2) to Hex tlie metatarso-phalangeal joint of the httle toe. 



The usual action of the muscle will be a combination of tliese two movements. 



Relations. — Superficially, the plantar fascia, the flexor brevis digitorum, and 

 even a sinall portion of the abductor hallucis. Deeply, the accessorius, flexor 

 brevis minimi digiti, long plantar ligament, and peroneus longus tendon. 



Variations. — The muscular slip attached to the base of the fifth metatarsal bone is often so 

 distinct as to form a separate muscle, tlie abductor ossis metatarsi quinti. 



Second Layer 



The second layer consists of the flexor accessorius muscle, the four lumbricales, 

 and the tendons of the flexor longus hallucis and the flexor longus digitorum. 



1. FLEXOR ACCESSORIUS DIGITORUM PEDIS 



The flexor accessorius digitorum pedis — named from its accessory or supple- 

 mentary action in assisting the flexion of the toes by the flexor longus digitorum — 

 is a dou))le-headed quadrilateral sheet. 



Origin. — Inner head : The whole of the concave inner surface of the calcaneum 

 below the groove for the flexor longus hallucis. 



Outer head : (1) The junction of the lower and outer surfaces of the calcaneum 

 in front of the lesser tubercle; (2) the under surface of the back part of the long 

 plantar ligament. 



Insertion. — The upper surface and outer border of the flexor longus digitorum 

 tendon about midway between the tubercles of the calcaneum and the heads of the 

 metatarsal bones. 



Structure. — Its inner head consists of fleshy fi})res which converge from their 

 origin in a somewhat fan-shaped sheet, and are joined shortly before their insertion 

 into the tendon by the outer head, which consists of a pointed tendinous origin, 

 from which the fleshy fibres form a somewhat smaller fan-shaped sheet which 

 blends with that from the inner head, to be inserted by fleshy fibres upon the 

 upper surface and outer border of the flexor longus digitorum, at its point of 

 division into the tendons for the four outer toes. 



Nerve-supply. — From the external plantar division of the posterior tibial 

 ncrvi', by l)ranches which enter the under surface of the muscle near its origin. 



Action.— To help in the flexion of the last phalanges of the four outer toes, 

 and at the same time to draw the toes somewhat outwards. On accovmt of the 

 oblicjue direction of the tendons of the flexor longus digitorum in the foot, they 

 would tend in flexing the toes to draw them at the same time inwards. This 

 tendency Avill be somewhat neutralised by the simultaneous contraction of the 

 accessorius. The accessorius will also be able to flex the toes Avhcn, on account of 

 the extensi(Mi of the ankle-joint, the muscular fibres of the flexor longus digitorum 

 are so relaxed as to be weakened in their action. 



Relations. — Superficially, the flexor brevis digitorum, the aVxluctor minimi 

 digiti, the tendons of the flexor longus digitorum and flexor longus hallucis, with 

 the external plantar vessels and nerve; deei)ly, the flexor brevis hallucis and long 

 plantar ligament. 



Variations. — An additional head may arise above the ankle from the flexor longus digitorum, 

 Hfxiir longus liallucis, or soleus. Sometimes the outer head is wanting, and occasionally the 

 whole muscle is absent. The (listril)Utinn of its filires to the tendons of the long flexor is very 

 variable. ' It may send fibres to the tenilon of the flexor longus hallucis. 



