ANNULAR LIGAMENTS OF THE ANKLE. 295 



layer of fascia is stretched from side to side across the limb known as the 

 deep fascia of the leg. Where covered by the solens 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 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. These bands 

 being merely stronger portions of the ordinary fascia, it is often difficult 

 in dissection to mark satisfactorily the exact line of their upper and lower 

 margins. They serve as retinacula, confining the tendons in their natural 

 positions. 



The anterior annular ligament includes two structures, one placed on the 

 lower part of the leg, the other opposite the bend of the ankle. The upper 

 band, ligamentum transversum cruris (Henle), of considerable breadth, 

 stretches from the lower end of the fibula to the lower end of the tibia, and 

 binds down the vertical portion of the extensor tendons as they turn forwards 

 to the foot : the sheath for the tendon of the tibialis anticus is distinct from 

 the others. The lower band., ligamentum cruciatum cruris (Henle), presents 

 superficially the appearance of the letter Y placed upon its side, being single 

 in its outer half, and usually divided into two branches internally. The 

 outer portion consists of a strong loop of fibres arising from the fore part of 

 the os calcis, completely surrounding the peroneus tertius and extensor 

 longus digitorum muscles, and inserted into the fore part of the os calcis, 

 deep in the hollow between that bone and the astragalus. Less regular is 

 the arrangement of the bands which pass from the extremity of the loop to 

 the inside of the foot : the strongest and most constant band passes super- 

 ficial to the extensor pollicis and on the deep surface of the tibialis anticus 

 muscle, only a few fibres passing superficial to the latter ; while another 

 band, lower down, is inserted into the inner side of the foot, in front of the 

 ankle, after crossing both those tendons. 



The loop formed by the outer part of this ligament derives additional interest from 

 being present in the lower animals, as may be well seen in the dog or cat, and in the 

 horse. 



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 

 deep layer), is very imperfectly defined ; and its lower border, giving 

 origin to many fibres of the abductor pollicis, is but little more distinct. 

 Its anterior extremity is attached to the inner malleolus, and its posterior 

 termination is inserted into the inner margin 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 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 pollicis. 



The external annular ligament extends from the point of the outer mal- 

 leolus to the outer surface of the calcaneum, and keeps in place the tendons 

 of the long and short peronei muscles. The tendons are close together, 

 and are surrounded by one synovial sac. 



