MUSCLES OF FOOT 491 



the second phalanx of the big toe on the first, and, less energetically, the first on the metatarsal. 

 It also inverts the foot. All three muscles extend the foot. The flexor hallucis is the strongest 

 of the three in this respect. 



Variations. — The muscles of the group may be more or less fused with one another or be 

 united by fascicuh. This is especially common between the two flexors of the toes. The 

 individual muscles vary in development. The flexor digitorum longus may be more or less 

 divided into separate fasciculi for the individual toes. The slip from the flexor hallucis longus 

 to the flexor digitorum longus varies greatly in extent, but usually passes mainly to the second 

 and third toes, more rarely to the second, third, and fourth, and very rarely to the fifth. In 

 most of the apes the tibial flexor (flejsor digitorum) sends tendons to the second and fifth, the 

 fibular flexor (flexor hallucis) to the first, third, and fourth toes. This condition is also some- 

 times found in man. A slip may pass from the tendon of the flexor digitorum to that of the 

 flexor hallucis longus. There may be a sesamoid bone in the tendon of the flexor hallucis 

 longus as it passes over the talus (astragalus) and calcaneus. The tibialis posterior may be 

 doubled. Aberrant fasciculi may arise from various regions on the back of the leg and join any 

 one of the three muscles of the group. 



Abnormal muscles. — The soleus accessorius. — Arises by a tendon from the head of the fibula 

 beneath the soleus. It is usually a slender muscle inserted into the medial surface of cal- 

 caneus. The tibialis secundus (tensor of capsule of ankle-joint). — A small muscle which 

 arises from the tibia beneath the flexor digitorum and is inserted into the capsule of the ankle- 

 joint. The fibulo -calcaneus medialis (peroneo-calcaneus internus of MacAlister, flexor 

 accessorius long. dig. long., etc.). — A fasciculus which arises from the lower third of the body of 

 the fibula and gives rise to a tendon which passes beneath the laciniate ligament to the quadratus 

 plantse or to the tendon of the flexor digitorum longus. 



BURS^ 



B. subtendinea m. tibialis posterioris. — A small bursa between the navicular fibro-cartilage 

 and the tendon. 



Synovial Tendon-sheaths 



Vagina m. fiexoris digitorum longi. — The tendon is surrounded by a synovial sheath 

 from the back of the medial malleolus to where it crosses the tendon of the flexor hallucis longus 

 below the navicular bone. It may communicate with the sheath of the tibialis anterior or with 

 that of the flexor hallucis longus. Vaginae tendinum digitales. — The tendons of the long 

 flexor, together with those of the short flexor, are surrounded by synovial sheaths from the 

 heads of the metatarsals to the insertions of the tendons. In structure these resemble those 

 of the fingers. Vagina m. flexoris hallucis longi. — The tendon is surrounded by a sheath 

 from the back of the medial malleolus to the crossing of the tendon of the flexor digitorum 

 longus. Another sheath surrounds the tendon from the middle of the first metatarsal to its 

 insertion. Vagina m. tibialis posterioris. — The tendon is surrounded by a synovial sheath ex- 

 tending from a region proximal to the medial malleolus to the insertion of the tendon. 



D. MUSCULATURE OF THE FOOT 



On the dorsum of the foot there is a muscle not represented in the hand, the 

 extensor digitorum brevis (fig. 418). In the sole of the foot there is a highly 

 developed musculature which may be subdivided into the flexor digitorum brevis 

 (fig. 419) ; the muscles connected with the long extensor of the toes, quadratus 

 plantse and lumbricales (fig. 420) ; the intrinsic muscles of the great toe, (figs. 

 419, 421); the intrinsic muscles of the little toe (figs. 419, 421); and the inter- 

 osseous muscles (fig. 422). These muscles abduct and adduct the toes, flex them 

 at the metacarpophalangeal joints and flex and extend them at the first row of 

 interphalangeal joints. On the second row of interphalangeal joints they seem 

 to exert relatively little action. All the movements, excepting flexion, are weak 

 in most individuals. The extensor digitorum brevis is innervated by the deep 

 peroneal (anterior tibial) nerve. The muscles of the sole of the foot are all 

 innervated by the lateral (external) plantar, except the flexor digitorum brevis, 

 the most medial of the lumbrical muscles, and the abductor and flexor brevis of 

 the great toe, which are innervated by the medial (internal) plantar. 



FASCIA 



Tela subcutanea. — Over the dorsum of the foot the tela subcutanea contains little fat. On 

 the sole of the foot and the plantar surface of the toes it contains much fat embedded in 

 dense fibrous tissue. 



Muscle fasciae. — Over the dorsum of the foot a fascial membrane extends from the 

 cruciate ligament mentioned above to the toes, where it is continued as fibrous sheaths for 

 the extensor tendons. Laterally and medially it is continued into the plantar fascia. Where 



