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of the external malleolus. It is directed out above, then back, 

 then slightly inward below. It separates the peronei from the 

 flexor muscles. The posterointernal border, or oblique line, 

 commences inside the head, and ends by joining the interosseous 

 ridge in the lower fourth of the bone. 



The anterior surface is very narrow above, broader and 

 grooved below; to it are attached the extensor proprius pollicis 

 pedis (extensor proprius hallucis), the extensor longus digi- 

 torum, and the peroneus tertius. 



The external surface is directed outward above and back- 

 ward below, and is occupied by the peroneus brevis and longus 

 muscles. 



The internal surface between the anterointernal and postero- 

 internal borders is grooved for the tibialis posticus. 



The posterior surface looks backward above and directly 

 inward below. Its upper third attaches the soleus muscle; its 

 lower part is rough for interosseous ligaments; to the rest of the 

 surface is attached the flexor longus pollicis. The medullary 

 canal opens on this surface and is directed downward. 



THE BONES OF THE FOOT 



The tarsus is composed of seven bones the calcaneum, or 

 os calcis, and the astragalus, the navicular, or scaphoid, three 

 cuneiform, and cuboid, 



The Os Calcis 



The os calcis (heel) is the largest bone of the foot; it articulates 

 with the astragalus above and cuboid in front. The bone 

 presents six surfaces. The posterior extremity, or tuberosity, 

 presents inferiorly two tubercles; the inner is the larger. Its 

 posterior surface presents three districts a smooth one above 

 for a bursa, a ligamentous one for the tendo Achillis, and a 

 lower convex part for the pad of the heel. The part in front 

 of the tuberosity forms a slightly constricted neck. 



The internal surface is deeply concave, and surmounted 

 above by the sustentaculum tali (support of the talus, i. e., 

 ankle bone or astragalus); this projects inward on a level 

 with the upper surface, and is grooved beneath for the flexor 



