THE INTEROSSEOUS MUSCLES 239 



Nerves. Extensor brevis by the anterior tibial. Flexor 

 brevis digitorum, abductor and flexor brevis hallucis, and 

 innermost lumbricalis by the internal plantar; all the others 

 by the external plantar. 



Actions. Popliteus flexes the knee and rotates the leg in, 

 pulls on the capsule of the joint, and keeps the popliteal bursa 

 open. The dorsum of the foot and anterior surface of the leg 

 is the extensor surface; the opposite side is the flexor surface, 

 so that raising the foot on the front of the leg is really extension, 

 and depressing it is flexion; it is customary to apply reverse 

 terms to these acts. 



Gastrocncmius flexes the knee, extends the ankle, combines 

 with the soleus and lifts the heel or raises the body on toes. 



Tibialis anticus and peroneus tertius flex the ankle; the 

 former rotates ii>, adducts, raises the first metatarsal bone. 



Tibialis posticus, peroneus longus and brevis are extensors. 

 Tibialis posticus and flexors of the toes rotate the foot in. 

 The three peronei and extensors of the toes rotate out. 



Peroneus longus strengthens the transverse arch, lifts the 

 outer border of the foot in walking, extends the foot, depresses 

 the first metatarsal, abducts the forefoot, rotates out. 



Flexors and extensors of the toes, interossei, and lumbricales 

 act as do the corresponding muscles of the hand. 



Flexor accessorius modifies the action of the flexor longus 

 digitorum, as those tendons cannot enter the foot in a straight 

 line. 



The extensor brevis digitorum does the same for the extensor 

 communis, though here they are not so much needed, and their 

 function is not so evident. 



Extensors of the foot slightly rotate in; flexors of the foot 

 slightly rotate out; plantaris indirectly pulls up the capsule 

 of the ankle-joint and slightly aids the gastrocnemius. 



Flexors of the Foot. Extensors of the Foot. 



Tibialis anticus. Tendo Achillis. 



Extensor communis digitorum. Peroneus longus and brevis. 

 Extensor proprius hallucis. Tibialis posticus. 



Peroneus tertius. Flexor longus digitorum and 



hallucis. 



