THE ANKLE 



1463 



share in maintaining the longitudinal arch of the foot. The flexors not only act upon the toes, 

 but aid the calf muscles in straightening the foot upon the leg in walking or standing upon tip- 

 toe; hence the value of educating them in cases of flat-foot. 



(D) Tendons on the lateral aspect. — The tendons of the two peronei, which 

 arise from the fibula between the extensor digitorum longus and flexor haUucis 

 longus, pass behind the lateral malleolus, the brevis being nearer to the bone (fig. 

 1177). They then pass forward over the lateral surface of the calcaneus, sepa- 

 rated by the peroneal tubercle when present, and diverge. 



The brevis — -the upper one — passes to the projection at the base of the fifth metatarsal; 

 the longus, lying below the brevis on the calcaneus, winds round the lateral border of the foot, 

 grooving the'lateral border and under surface of the cuboid. Finally, crossing the sole obliquely 

 forward and medially, it is inserted into the adjacent parts of the first cuneiform and the back 

 part and under surface of the first metatarsal. While in connection with the under surface of 

 the cuboid, this tendon is covered in by a sheath from the long plantar hgament, and often 

 contains a sesamoid bone. The two peronei evert the foot, as is seen in talipes valgus and in 

 fracture of the lower end of the fibula; the peroneus longus aids in the support of the arch of the 

 foot (p. 1466), and, by keeping the great toe on the ground, is important in the third stage of 

 walking, skating, etc. 



Annular ligaments and synovial membranes of tendons. — These strap-like 

 bands of deep fascia, which serve to keep the above tendons in position, are three 

 in number, viz.: — 



(A) Lateral. — This, the superior peroneal retinaculum, extends from the tip 

 of the lateral malleolus to the lateral surface of the calcaneus. It keeps the two 



Fig. 1178. — Relations of Parts behind the Medial Malleolus. (Heath.) 



Tibialis posterior 

 Cruciate ligament 



Tibialis posterior 

 Tibialis anterior 



Tendo Achillis 



Flexor digitorum longus 

 Posterior tibial artery 

 Tibial nerve 



Fexor digitorum longus 



peronei in place, and surrounds them behind the fibula in one sheath with a single 

 synovial sac, which extends upward into the leg for 3 . 7 cm. (1^ in.), and sends two 

 processes into the two sheaths in which the tendons lie on the calcaneus. Farther 

 on, while in relation with the cuboid, the peroneus longus has a second synovial 

 sheath. 



(B) Medial. — This, the laciniate ligament, crosses from the medial malleolus 

 to the medial surface of the calcaneus. Beneath it are the following canals: — (1) 

 For the tibialis posterior. This tendon-sheath is lined by a synovial membrane 

 extending from a point 3 . 7 cm. (1| in.) above the malleolus to the navicular. (2) 

 For the flexor digitorum longus. The synovial sheath of this tendon is separate 

 from that of the closely contiguous tibialis posterior. It extends upward into the 

 leg about as high as the sheath just given. It reaches down into the sole of the 

 foot; but where the tendon subdivides to enter the thecse, each of these is hned by 

 a separate synovial sheath. Next comes (3) a wide space for the posterior tibial 

 vessels and nerve; and, lastly, (4) a canal, like the other two, with a separate 

 synovial sheath, for the tendon of the flexor hallucis longus. The lower margin of 

 this annular ligament gives an attachment to the abductor hallucis and blends 

 with the plantar fascia. The medial calcaneal vessels and nerve perforate the 

 ligament. 



