TIBIALIS POSTICUS. 



239 



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 superfi- 

 cially to it, and it crosses the tendon of the flexor longus pollicis. 

 At the point of crossing it receives the tendinous slip of communi- 

 cation 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 extent of the tibialis posticus. 



The Tibialis poslicus (extensor tarsi tibialis) lies upon the interos- 

 seous membrane, between the two bones of the leg. 

 It arises by two heads from the adjacent sides of Fi g- 94< * 

 the tibia and fibula their whole length, and from 

 the interosseous membrane. Its tendon passes 

 inwards beneath the .tendon of the flexor longus 

 digitorum, arid runs in the same sheath; it then 

 passes through a proper sheath over the deltoid liga- 

 ment, and beneath the calcaneo-scaphoid articula- 

 tion, 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 in- 

 termuscular 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 mus- 

 cles change their relative position to each other in 

 their course. Thus, in the leg, the position of the 

 three muscles from within outwards, is flexor 



* The deep layer of muscles of the posterior tibial region. 1. The lower extremity 

 of the femur. 2. The ligamentum posticum Winslowii. 3. The tendon of the semi- 

 membranosus muscle dividing into its three slips. 4. The internal lateral ligament of 

 the knee-joint. 5. The external lateral ligament. 6. The popliteus muscle. 7. The 

 flexor longus digitorum. 8. The tibialis posticus.. 9. The flexor longus pollicis. 10. 

 The peroneus longus muscle. 11. The peroneus brevis. 12. The tendo Achillis 

 divided at its insertion into the os calcis. 13. The tendons of the tibialis posticus and 

 flexor longus digitorum muscles, just as they are about to pass beneath the internal 

 annular ligament of the ankle ; the interval between the latter tendon and the tendon 

 of the flexor longus pollicis is occupied by the posterior tibial vessels and nerve. 



