43 THE INFERIOR EXTREMITY 



forwards, from the medial border of the groove on the talus 

 for the flexor hallucis longus to the sustentaculum tali. 



The posterior talo-calcanean ligament passes from the pos- 

 terior border of the talus to the calcaneus. It closes the 

 posterior talo-calcanean articulation behind. 



The dorsal talo-navicular ligament extends, on the dorsum 

 of the foot, from the head of the talus to the navicular 

 bone. It is thin and membranous. 



The medial and lateral parts of the capsule of the ankle 

 joint also help to keep the talus in its place. 



Dissection. Divide the various ligaments which hold the 

 talus in place, and remove the bone. When that has been done 

 the different parts which form the socket for the head of the 

 talus can be examined, and it will be obvious that the posterior 

 talo-calcanean articulation is completely cut off from the anterior 

 by the strong interosseous talo-calcanean ligament. The great 

 strength of that ligament can now be appreciated, and the three 

 facets on the head of the talus studied : (i) a convex 'surf ace 

 which looks forwards and articulates with the navicular ; (2) 

 an elongated facet on its plantar aspect (sometimes divided into 

 two), which rests upon the sustentaculum tali ; and (3) between 

 i and 2, a triangular facet which corresponds with the dorsal 

 surface of the plantar calcaneo-navicular ligament. In the 

 recent state (and indeed usually also in the macerated condition 

 of the bone) these three facets are very distinctly mapped off 

 from each other by intervening ridges. 



Calcaneo-navicular Ligaments. Although the calcaneus 

 does not directly articulate with the navicular bone, it is 

 connected with it by two powerful ligaments, viz., a plantar 

 calcaneo-navicular ligament and the calcaneo-navicular part 

 of the bifurcate ligament. 



The upper surface of the plantar calcaneo-navicular ligament 

 (O.T. inferior cakaneo-scaphoid ligament} is brought into view 

 by the removal of the talus. It fills up the angular gap 

 between the sustentaculum tali and the navicular bone, and 

 enters into the formation of the socket for the head of the 

 talus (Fig. 198). Its upper surface is smooth and covered 

 with a synovial layer ; its plantar surface is supported 

 by the tendon of the tibialis posterior. This ligament 

 has an important part to play in maintaining the integrity 

 of the longitudinal arch of the foot. Posteriorly it is 

 attached to the anterior border of the sustentaculum tali, 

 whilst anteriorly it is fixed to the plantar surface of the 

 navicular bone. 



The calcaneo-navicular part of the bifurcate ligament (O.T. 



