538 THE MUSCLES AND FASCIAE 



tinct synovial sheath. The Y-shaped portion is placed in front of the ankle- 

 joint, the stem of the Y, the fundiform ligament of Retzius, being attached externally 

 to the upper surface of the os calcis, in front of the depression for the interosseous 

 ligament; it is directed inward, as a double layer, one lamina passing in front, 

 and the other behind, the tendons of the Peroneus tertius and Extensor longus 

 digitorum. At the inner border of the latter tendon these two layers join, 

 forming a sheath in which the tendons are enclosed, surrounded by a synovial 

 membrane. From the inner extremity of this sheath the two limbs of the Y 

 diverge; one passes upward and inward, to be attached to the internal malleolus, 

 passing over the Extensor proprius hallucis and the vessels and nerves, but en- 

 closing the Tibialis anticus and its synovial sheath by a splitting of its fibres. The 

 other limb extends downward and inward to be attached to the inner border of 

 the plantar fascia, and passes over the tendons of the Extensor proprius hallucis 

 and Tibialis anticus and also the vessels and nerves. These two tendons are con- 

 tained in separate synovial sheaths situated beneath the ligament. 



The Internal Annular Ligament (ligamentum laciniatum) is a strong fibrous 

 band which extends from the inner malleolus above to the internal margin of the 

 os calcis below, converting a series of grooves in this situation into canals for the 

 passage of the tendons of the Flexor muscles and vessels into the sole of the foot. 

 It is continuous by its upper border with the deep fascia of the leg, and by its lower 

 border with the plantar fascia and the fibres of origin of the Abductor hallucis 

 muscle. The four canals which the ligament completes transmit, counting from 

 before backward, first, the tendon of the Tibialis posticus; second, the tendon of 

 the Flexor longus digitorum; third, the posterior tibial vessels and nerve, which 

 run through a broad space beneath the ligament ; lastly, in a canal formed partly by 

 the astragalus, the tendon of the Flexor longus hallucis. The canals for the tendons 

 are lined by a separate synovial membrane. 



The External Annular Ligament is divided into two portions- a superior portion 

 (retinaculum mm. peronaeorum superius), which extends from the extremity of 

 the outer malleolus to the outer surface of the os calcis; it binds down the tendons 

 of the Peroneus longus and brevis muscles in their passage behind the external 

 malleolus. The two tendons are enclosed in one synovial sac. An inferior portion 

 (retinaculum mm. peronaeorum inferius), which bridges the Peronei on the side of 

 the os calcis and is attached to the bone above and below them, 



8. The Dorsal Region (Fig. 393). 



Extensor brevis digitorum. 



Fascia (fascia dorsalis pedis). The fascia on the dorsum of the foot is a thin 

 membranous layer continuous above with the anterior margin of the annular 

 ligament; it becomes gradually lost opposite the heads of the metatarsal bones, 

 and on each side blends with the lateral portions of the plantar fascia; it forms a 

 sheath for the tendons placed on the dorsum of the foot. On the removal of this 

 fascia the muscle and tendons of the dorsal region of the foot are exposed. 



The Extensor brevis digitorum (TO. extensor digitorum brevis} (Fig. 393) is 

 a broad thin muscle which arises from the fore part of the upper and outer sur- 

 faces of the os calcis, in front of the groove for the Peroneus brevis, from the exter- 

 nal calcaneo-astragaloid ligament, and from the common limb of the Y-shaped 

 portion of the anterior annular ligament. It passes obliquely across the dorsum 

 of the foot, and terminates in four tendons. The innermost, which is the largest, 

 is inserted into the dorsal surface of the base of the first phalanx of the great toe, 

 crossing the dorsalis pedis artery; the other three, into the outer sides of the long 

 Extensor tendons of the second, third, and fourth toes. 



