THE ASTRAGALUS 107 



longus hallucis. The superior surface has two articular facets, 

 separated by a groove which runs forward and outward for 

 the interosseous ligament. The anterior facet, often subdivided 

 into two, is on the sustentaculum, and is concave longitudinally; 

 the other one is convex. At the forepart of the groove is a 

 roughness for the extensor brevis digitorum. Behind the 

 articular surfaces is a region convex from side to side and 

 concave from before backward; above it is placed adipose 

 tissue in front of the tendo Achillis. 



The anterior surface is concavoconvex for articulation with 

 the cuboid. 



The inferior surface, in front of the tuberosity, projects in 

 an anterior tubercle with a transverse groove in front, and 

 gives attachment to an inferior calcaneocuboid ligament. 



The external surface is usually flat, and presents near the 

 centre a tubercle for the middle fasciculus of the external 

 lateral ligament, and anteriorly often a peroneal spine, separat- 

 ing two grooves the upper for the peroneus brevis tendon, 

 the lower for that of the peroneus longus. 



The Astragalus 



The astragalus (a die), or jtalus, receives the weight of the 

 body from the leg. It articulates with four bones the tibia 

 above and internally, the fibula externally, os calcis below, 

 and scaphoid in front. Its long axis is forward and inward. 

 The main part is the body, the convex anterior portion the 

 head, just behind which is the neck. 



The superior articular surface occupies the whole of the 

 upper surface of the body and sends a prolongation down on 

 either side. The trochlear part is convex from below back- 

 ward, and slightly concave from side to side, wider in front 

 than behind; its outer margin is longer than the inner, and 

 curved, while the inner is straight. The inner lateral part is 

 sickle-shaped for the internal malleolus; the outer lateral part 

 is concave and triangular, and articulates with the external 

 malleolus. Inferiorly there are two articular surfaces for the 

 calcaneum ; the posterior one is concave, separated by the 

 interosseous groove from the anterior one, which is convex. 

 The head articulates anteriorly with the scaphoid; at the lower 

 and inner part, between this and the anterior articulation for 



