The axis of rotation at the ankle joint in man; its influence upon the form of the talus and the mobility of the fibula.

The upper articular surface of the talus is customarily described as wedge-shaped, its width diminishing from front to back. Measurements indicate that the majority of tali do, in fact, show some narrowing of this surface, but that the triangular facet at its lateral margin-articulating with the inferior transverse tibio-fibular ligament -often gives a misleading impression as to the true reduction in width (Inkster, 1927). A simple index of the degree of 'wedging' of any particular talus is obtained if this reduction (x) is divided by the length of the trochlear surface (y). To assess the variations of 'wedging' in different specimens, 164 cartilage-covered tali-nine from fresh amputations, the remainder from dissecting-room subjects-were examined. Twelve proved unsuitable for detailed study, mainly due to osteo-arthritic changes which obliterated the contours, and this paper is therefore based upon analysis of 152 specimens. For obvious reasons no dried bones are included in this series. the each talus were measured at right angles to the medial edge; the anterior measurement was taken at the level of the front of the lateral edge, and the posterior measurement at the posterior limit of the medial articular surface. To measure the length of the trochlear surface a line was taken, parallel to its medial edge, from the point where the medial side of the triangular facet meets the posterior articular margin. The distance between the anterior and posterior limits of the articular cartilage was measured along this line. degree