FIBULAR REGION. 257 



connected with a groove in the astragalus and os calcis, into the sole of 

 the foot, where it divides into four tendons, which are inserted into the 

 base of the last phalanx of the four lesser toes, perforating the tendons of 

 the flexor brevis digitorum. 



Relations. By its superficial surface with the intermuscular fascia, 

 which separates it from the soleus, and with the posterior tibial vessels and 

 nerve. By its deep surface with the tibia and tibialis posticus. In the sole 

 of the foot its tendon is in relation with the abductor pollicis and flexor 

 brevis digitorum, which lie superficially to it, and it crosses the tendon of 

 the flexor longus pollicis. At the point of crossing it receives the tendi- 

 nous slip of communication from the latter. 



The flexor longus pollicis must now be removed from its origin, and 

 the flexor longus digitorum drawn aside, to bring into view the entire ex- 

 tent of the tibialis posticus. 



The TIBIALIS POSTICUS (extensor tarsi tibialis) lies upon the interosseous 

 membrane, between the two bones of the leg. It arises by two heads from 

 the adjacent sides of the tibia and fibula their whole length, and from the 

 interosseous membrane. Its tendon passes inwards beneath the tendon 

 of the flexor longus digitorum, and runs in the same sheath; it then passes 

 through a proper sheath over the deltoid ligament, and beneath the calca- 

 neo-scaphoid articulation to be inserted into the tuberosity of the scaphoid 

 and internal cuneiform bone. While in the common sheath behind the 

 internal malleolus, the tendon of the tibialis posticus lies internally to that 

 of the flexor longus digitorum, from which it is separated by a thin fibrous 

 partition. A sesamoid bone is usually met with in the tendon close to its 

 insertion. 



Relations. By its superficial surface with the intermuscular septum, 

 the flexor longus pollicis, flexor longus digitorum, posterior tibial vessels 

 and nerve, peroneal vessels, and in the sole of the foot with the abductor 

 pollicis. By its deep surface with the interosseous membrane, the fibula 

 and tibia, the ankle joint, and the astragalus. The anterior tibial artery 

 passes between the two heads of the muscle. 



The student will observe that the two latter muscles change their rela- 

 tive position to each other in their course. Thus, in the leg, the position 

 of the three muscles from within outwards, is, flexor longus digitorum, 

 tibialis posticus, flexor longus pollicis. At the inner malleolus, the rela- 

 tion of the tendons is, tibialis posticus, flexor longus digitorum, both 

 in the same sheath; then a broad groove, which lodges the posterior 

 tibial artery, vense comites, and nerve ; and lastly, the flexor longus 

 pollicis. 



Actions. The popliteus is a flexor of the tibia upon the thigh, carrying 

 it at the same time inwards, so as to invert the leg. The flexor longus 

 pollicis and flexor longus digitorum are the long flexors of the toes ; their 

 tendons are connected in the foot by a short tendinous band, hence they 

 necessarily act together. The tibialis posticus is an extensor of the tarsu 

 upon the leg, and an antagonist to the tibialis anticus. It combines with 

 the tibialis anticus in adduction of the foot. 



Fibular Region. 



Peroneus longus, 

 '- Pero'neus brevis. 



22* * 



