302 THE ARTICULATIONS 



It is better marked, deeper, and broader laterally. Stroijg laminte extend from the rough 

 inferior and lateral surfaces of the neck of the talus to the rough superior surface of the calcaneus 

 anteriorly, forming the posterior boundary of the anterior talo-calcaneal joint; these have been 

 described as the anterior (interosseous) ligament. The posterior laminse extend from the roof 

 of the sinus pedis to the calcaneus immediately in front of the lateral facet, thus forming the 

 anterior part of the capsule of the posterior joint. 



The lateral talo-calcaneal ligament (fig. 334) extends from the groove just below and in 

 front of the lateral articular facet of the talus, to the calcaneus some little distance from the articu- 

 lar margin. Its fibres are nearly parallel with those of the calcaneo-fibular ligament of the 

 ankle, which passes over it and adds to its strength. It fills up the interval between the calcaneo- 

 fibular and anterior talo-fibular ligaments, a considerable bundle of its fibres blending with the 

 anterior border of the calcaneo-fibular. 



The posterior talo-calcaneal ligament passes from the lateral tubercle of the talus and lower 

 edge of the groove for the flexor hallucis longus to the calcaneus, a variable distance from the 

 articular margin. 



The medial talo-calcaneal ligament includes two portions. The first is a narrow band of 

 weU-marked fibres passing obliquely downward and forward from the medial tubercle of the 

 talus, just behind the medial end of the sinus tarsi, to the calcaneus behind the sustentaculum 

 tali, thus completing the floor of the groove for the flexor hallucis longus tendon. The second 

 portion, which is often considered a separate ligament, is described below with the anterior 

 talo-calcaneal joint. 



The synovial sac is distinct from any other. 



The nerve-supply is from the posterior tibial or one of its plantar branches. 



The arteries are, a branch from the posterior tibial, which enters at the medial end of the 

 sinus pedis; and twigs from the tarsal, lateral malleolar, and the peroneal, which enter at the 

 lateral end of the sinus. 



(ii) The Anterior Talo-calcaneal Joint 



Class. — Diarthrosis. Subdivision. — Arthrodia. 



This joint is formed by the anterior facet on the upper surface of the calcaneus 

 and the facets on the lower surface of the neck and head of the talus; it is bounded 

 on the sides and behind by ligaments, and communicates anteriorly with the 

 talo-navicular joint. The ligaments are: — 



Interosseous. Medial talo-calcaneal. 



Lateral calcaneo-navicular. 



The interosseous ligament by its anterior laminse limits this joint posteriorly. It has been 

 already described. 



The medial talo-calcaneal ligament (second portion; see above) consists of short fibres at- 

 tached above to the medial surface of the neck of the talus, and below to the upper edge of the 

 free border of the sustentaculum tali, blending posteriorly with the medial extremityof the inter- 

 osseous ligament, and anteriorly with the upper border of the plantar calcaneo-navicular liga- 

 ment. It is strengthened by the deltoid ligament, the anterior fibres of which are also attached 

 to the plantar calcaneo-navicular ligament. 



The lateral calcaneo-navicular (figs. 334 and 335) limits this, as well as the talo-navicular 

 joint, on the lateral side. It is a strong, well-marked laand, extending from the rough upper sur- 

 face of the calcaneus, lateral to the anterior facet, to a slight groove on the lateral surface of 

 the navicular near the posterior margin. It blends below with the plantar calcaneo-navicular, 

 and above with the talo-navicular ligament. Its fibres run obliquely forward and medially. 

 The deltoid ligament and middle fasciculus of the lateral ligament of the ankle-joint also add 

 to the security of these two joints, and assist in limiting movements between the bones by pass- 

 ing over the talus to the calcaneus. 



The synovial membrane is the same as that of the talo-navicular joint. The arteries and 

 nerves are derived from the same sources as those of the medio-tarsal joints. 



The movements of which these two joints are capable are adduction and abduction, with 

 some amount of rotation. Adduction, or inclination of the sole medialward, is combined with 

 some medial rotation of the toes, and some lateral rotation of the heel; while abduction, or in- 

 clination of the foot lateralward, is associated with turning of the toes laterally and the heel 

 medially. Thus the variety and the range of movements of the foot on the leg, which at the ankle 

 are almost limited to lk;xion and extension, are increased. The cuboid moves with the calca- 

 neus, while the navicular revolves on the head of the talus. 



In walking, the heel is first placed on the ground; the foot is slightly adducted; but as the 

 body swings forward, finst, the lateral then the medial toes touch the ground, the talus presses 

 against the navicular and sinks upon the plantar calcaneo-navicular ligament; the foot then 

 becomes slightly abducted. When the foot is firmly placed on the ground, the weight is trans- 

 mitted to it obliciucly downward and medially, so that if the ligaments between the calcaneus 

 and talus did not check abduction, medial displacement of the talus from the tibio-fibular arch 

 would only be r)reventcd by the tendons passing round the medial aiikle (especially the tibialis 

 posterior). If the ligaments be too weak to limit al)duction, the weight of the body increases it, 

 and forces the medial malleolus and talus downward and medially, giving rise to flat foot. 



The advantag(!M of the obliquity and peculiar arrang(!nu!nt of the posterior talo- 

 calcaneal articulation are seen in walking: — (i) for the posterior facet of the calcaneus receives. 



