TARSUS. 749 



ular faces one anterior and small, the otlier posterior and 

 large, separated by a deep fossa for the interosseous liga- 

 ment, and both faces articulating with the os calcis. The 

 front of the astragalus is smooth and rounded for articula- 

 ting with the naviculare. The posterior is grooved for the 

 tendon of the flexor pollicis. Its outer surface is smooth 

 for articulating with the malleolus externus. Its inner 

 surface articulates with the malleolus internus. 



The os colds calx, the heel, (Fig. 243,) is readily dis- 

 tinguished by being the largest bone of the tarsus, and 

 being situated at its' posterior and lower part. Its form is 

 oblong. Its upper surface has two faces, separated by a 

 groove, for articulating with the astragalus. Its lower 

 surface is rather concave, and bounded posteriorly by two 

 tubercles which give attachment to the aponeurosis plan- 

 taris and muscles of the foot. Its anterior extremity artic- 

 ulates with the cuboides by a slightly concave surface. Its 

 posterior extremity is convex and rough, forms the heel, 

 has a bursa, and receives the insertion of the tendo Achittis. 

 Externally the calcis is rather flat and grooved for the pas- 

 sage of the peroneal tendons ; and internally it is hollowed 

 and arched for the passage of the flexor tendons, tibialis 

 posticus, and plantar vessels and nerves. It articulates 

 with the astragalus and cuboid. 



The o,s naviculare or scaplioides (Fig. 243) occupies a mid- 

 dle position at the upper and inner portion of the tarsus. 

 Its form is oval. Its posterior surface is concave and smooth 

 for articulating with the head of the astragalus. Its ante- 

 rior surface is divided into three articular facets for the three 

 cuneiform bones. Its inferior surface gives insertion to the 

 tibialis posticus, and its external articulates with the cuboid. 



This bone articulates with five, the astragalus, cuboid, 

 and three cuneiform bones. 



The os cuboides (Fig. 243) is situated on the outside of 

 the naviculare, and occupies the external and anterior por- 

 tion of the tarsus. Its form is somewhat cubical. Its up- 

 per surface is rough and flat ; its lower, irregular, rough, 

 and grooved for the tendon of the peronetis-longus. Its 



