258 THE MUSCLES AND FASCIA OP THE LOWER LIMB. 



layer of fascia is stretched from side to side, binding down the deeper muscles to the 

 tibia and fibula. Where it is covered by the soleus and gastrocnemius, this fascia is 

 weak, but it becomes stronger as it escapes from under cover of those muscles and 

 approaches the malleoli. 



Below the ankle the deep fascia of the leg becomes continuous with that of the foot. 

 In front and on the sides of that joint, it is strengthened by broad bands of fibres, 

 which are called annular ligaments, and serve to confine the tendons in their positions. 



The anterior annular ligament includes two structures, one placed at the lower 

 part of the leg, the other opposite the bend of the ankle. The upper land, of consi- 

 derable breadth, stretches transversely from the anterior border of the fibula to the 

 corresponding part of the tibia, and binds down the vertical portion of the extensor 

 tendons as they descend to the foot : the tendon of the tibialis anticus alone has 

 a synovial sheath under this part of the ligament. The loiver land presents super- 

 ficially the appearance of the letter KJ placed thus upon its side, being single in its 

 outer half, and divided into two branches internally. The outer portion springs 

 from the hollow of the os calcis, between the outer end of the interosseous astragalo- 

 calcaneal ligament and the posterior articular surface for the astragalus, and forms a 

 strong loop (the fundiform ligament of Eetzius) which completely surrounds the pero- 

 neus tertius and extensor longus digitorum muscles. From the extremity of the loop 

 some of the fibres are continued into the two branches, which are, however, less 

 regular in their arrangement : the strongest and most constant band passes to the 

 internal malleolus, crossing over the extensor hallucis, and on the deep surface of the 

 tibialis anticus tendon, only a few fibres passing superficially to the latter ; while 

 the lower band, after crossing both those tendons is inserted on the inner side of the 

 foot into the fascia of the sole. The tendons are surrounded by three synovial 

 sheaths under this part of the ligament : one is common to the peroneus tertius and 

 extensor longus digitorum ; the second invests the extensor proprius hallucis ; and 

 the third, on the tibialis anticus, is continuous with that under the upper band of 

 the ligament. There is also in many cases a bursa between the fundiform ligament 

 and the outer side of the neck of the astragalus. 



The internal annular ligament crosses the space between the inner ankle and 

 the heel, through which the tendons of the flexor muscles run. Its upper border, 

 continuous with the fascia of the leg (more especially the intermuscular layer), is very 

 imperfectly defined ; and its lower border, giving origin to many fibres of the 

 abductor hallucis, is but little more distinct. Its anterior extremity is attached to the 

 inner malleolus, and its posterior to the inner side of the calcaneum ; but between 

 these two points it arches over several osseous grooves so as to form canals for the 

 passage of tendons. The first canal (next to the malleolus) contains the tendon of 

 the tibialis posticus, and the second that of the flexor longus digitorum, each being 

 provided with a synovial lining. Then follows a wider space for the passage of the 

 posterior tibial vessels and nerve. Lastly a fourth canal upon the astragalus, lined like 

 the first two by a synovial bursa, transmits the tendon of the flexor longus hallucis. 



The external annular ligament extends from the point of the outer malleolus 

 to the outer side of the calcaneum, and keeps in place the tendons of the long and 

 short peroneal muscles. The tendons are close together, and are surrounded by one 

 synovial sac. 



Subcutaneous bursae are sometimes developed over the malleoli, especially the 

 external, rarely over the lower end of the tendo Achillis. 1 



MUSCLES. The muscles of this part are divided naturally into three groups, 

 which occupy respectively the front, the outer side, and the back of the leg. 



1 Synnestvedt, "Beskrirelse af de paa Over- og Underextremiteterne forekommende Bursae mucosas." 

 Christiania, 1869. 



