THE POSTERIOR TIBIOFIBULAR REGION 535 



the foot (Fig. 399), where, crossing superficially to the tendon of the Flexor 

 longus hallucis, 1 to which it is connected by a strong tendinous slip, it becomes 

 expanded, is joined by the Flexor accessorms, and finally divides into four tendons, 

 which are inserted into the bases of the last phalanges of the four lesser toes, each 

 tendon passing through a fissure in the tendon of the Flexor brevis digitorum 

 opposite the base of the first phalanges (Fig. 398). 



Relations. In the leg, by its superficial surface, with the posterior tibial vessels and nerve, 

 and the deep transverse fascia, which separates it from the Soleus muscle; by its deep surface, 

 with the Tibia and Tibialis posticus. In the foot it is covered by the Abductor hallucis and 

 Flexor brevis digitorum, and crosses superficial to the Flexor longus hallucis. 



The Tibialis posticus (m. tibialis posterior) lies between the two preceding 

 muscles, and is the most deeply seated of all the muscles in the leg. It com- 

 mences above by two pointed processes, separated by an angular interval, through 

 which the anterior tibial vessels pass forward to the front of the leg. It arises 

 from the whole of the posterior surface of the interosseous membrane, excepting 

 its lowest part, from the outer portion of the posterior surface of the shaft of the 

 tibia, between the commencement of the oblique line above, and the junction 

 of the middle and lower third of the shaft below; and from the upper two-thirds 

 of the internal surface of the fibula; some fibres also arise from the deep transverse 

 fascia and from the intermuscular septa, separating it from the adjacent muscles 

 on each side. This muscle, in the lower fourth of the leg, passes in front of the 

 Flexor longus digitorum, and terminates in a tendon which passes through a groove 

 behind the inner malleolus with the tendon of that muscle, but enclosed in a separ- 

 ate sheath; it then passes through another sheath, over the internal lateral ligament 

 into the foot, and then beneath the inferior calcaneoscaphoid ligament. Beyond 

 this sheath the tendon passes between the sustentaculum tali and the tubercle of 

 the scaphoid to the plantar aspect and divides into two main slips. The stronger 

 medial slip is inserted into the tubercle of the scaphoid and into the internal cunei- 

 form and sends an expansion to the plantar surface of the sustentaculum tali. The 

 weaker lateral slip divides into lesser slips, which are inserted into the middle and 

 external cuneiform, the cuboid and the base of the second, third, and fourth meta- 

 tarsal bones. The stronger tendon as it passes over the scaphoid contains a 

 sesamoid bone. A bursa is often situated between the tendon and the scaphoid. 



Relations. By its superficial surface, with the Soleus, from which it is separated by the 

 deep transverse fascia, the Flexor longus digitorum, the posterior tibial vessels and nerve, and 

 the peroneal vessels; by its deep surface, with the interosseous ligament, the tibia, fibula, and 

 ankle-joint. 



Nerves. The Popliteus is supplied by the fourth and fifth lumbar and first sacral nerves, 

 through the internal popliteal; the Flexor longus digitorum and Tibialis posticus by the fifth 

 lumbar and first and second sacral; and the Flexor longus hallucis by the fifth lumbar and first 

 and second sacral nerves through the posterior tibial. 



Actions. The Popliteus assists in flexing the leg upon the thigh; when the leg is flexed, it 

 will rotate the tibia inward. It is especially called into action at the commencement of the act of 

 bending the knee, inasmuch as it produces a slight inward rotation of the tibia, which is essen- 

 tial in the early stages of this movement. The Tibialis posticus is a direct Extensor of the foot 

 at the ankle-joint; acting in conjunction with the Tibialis anticus, it turns the sole of the foot 

 inward (i. e., inverts the foot), antagonizing the Peronei, which turn it outward (evert it). In 

 the sole of the foot the tendon of the Tibialis posticus lies directly below the inferior calcaneo- 

 scaphoid ligament, and is therefore an important factor in maintaining the arch of the foot. 

 The Flexor longus digitorum and Flexor longus hallucis are the direct Flexors of the phalanges, 

 and, continuing their action, extend the foot upon the leg; they assist the Gastrocnemius and Soleus 

 in extending the foot, as in the act of walking or in standing on tiptoe. In consequence of the 

 oblique direction of the tendon of the long Flexor, the toes would be drawn inward were it not 

 for the Flexor accessorius muscle, which is inserted into the outer side of its tendon and draws 



1 That is, in the order of dissection of the sole of the foot. 



