independent bone called os trigonum or accessory talus; it may represent the tarsale proximale intermedium. On the bone's inferior side, three articular surfaces serve for the articulation with the calcaneus, and several variously developed articular surfaces exist for the articulation with ligaments. For descriptive purposes the talus bone is divided into three sections, neck, body, and head. Head The talus bone of the ankle joint connects the leg to the foot. The head of talus looks forward and medialward; its anterior articular or navicular surface is large, oval, and convex. Its inferior surface has two facets, which are best seen in the fresh condition. The medial, situated in front of the middle calcaneal facet, is convex, triangular, or semi-oval in shape, and rests on the plantar calcaneonavicular ligament; the lateral, named the anterior calcaneal articular surface, is somewhat flattened, and articulates with the facet on the upper surface of the anterior part of the calcaneus. Neck The neck of talus is directed anteromedially, and comprises the constricted portion of the bone between the body and the oval head. Its upper and medial surfaces are rough, for the attachment of ligaments; its lateral surface is concave and is continuous below with the deep groove for the interosseous talocalcaneal ligament. Body The body of the talus comprises most of the volume of the talus bone (ankle bone). It presents with five surfaces; a superior, inferior, medial, lateral and a posterior: The superior surface of the body presents, behind, a smooth trochlear surface, the trochlea, for articulation with the tibia. The trochlea is broader in front than behind, convex from before backward, slightly concave from side to side: in front it is continuous with the upper surface of the neck of the bone. the inferior surface presents two articular areas, the posterior and middle calcaneal surfaces, separated from one another by a deep groove, the sulcus tali. The groove runs obliquely forward and lateralward, becoming gradually broader and deeper in front: in the articulated foot it lies above a similar groove upon the upper surface of the calcaneus, and forms, with it, a canal (sinus tarsi) filled up in the fresh state by the interosseous talocalcaneal ligament. The posterior calcaneal articular surface is large and of an oval or oblong form. It articulates with the corresponding facet on the upper surface of the calcaneus, and is deeply concave in the direction of its