BONES. 



Lower Extremity (external malleolus). This is pyramidal. 

 The inner surface has a triangular facet which is plane antero- 

 posteriorly and slightly convex vertically ; behind this is a pit 

 for the posterior fasciculus of the external lateral ligament; 

 above the facet is a triangular area from whose summit the 

 interosseous ridge arises. The external surface is rounded and 

 continuous with the surface enclosed by the splitting of the 

 anterior border; it ends below in a pointed process which is 

 lower than that of the internal malleolus. The posterior sur- 

 face is broad above but narrow below, and is grooved. [238] 



Astragalus. This consists of a body, neck, and head; it lies 

 above the os calcis, wedged between the malleoli. Body. A 

 saddle-shaped facet (trochlea) , broadest in front, lies on the 

 upper surface. This is continuous, on the outer surface, with 

 a quadrant-shaped facet, concave vertically, whose inferior 

 angle (external process) is everted ; and on the inner surface 

 with a comma-shaped facet, below whose tail is a circular im- 

 pression for the internal lateral ligament. The preceding facets 

 articulate with the tibia and fibula. At the back of the inferior 

 surface is an oval concave facet (posterior calcanean) which is 

 placed obliquely ; in front of this a deep furrow runs forward 

 and outward ; in front of this is a small oval and convex facet 

 (middle calcanean). On the posterior surface a groove, run- 

 ning downward and inward, separates two tubercles. The 

 head is oval and directed forward and inward. On its anterior 

 surface is a convex facet, for the scaphoid, which is usually 

 confluent with the middle calcanean facet, though a small facet 

 (anterior calcanean) may intervene. On the inner and under 

 surface is a facet for the inferior calcaneo-navicular ligament. 

 The neck, best seen above, runs forward and slightly inward 

 from the body to the head ; it forms a wide groove externally 

 which joins the interosseous groove below. [239] 



Os Calcis. This lies posteriorly, under the astragalus. The 

 upper surface is rounded transversely behind ; in front of this 

 is a convex facet; in front of this a groove runs forward and 



[255] 



