OS CUBOIDES. OS CUNEIFORME EXTERNUM. 215 



The OS naviculare and astragalus are joined as a ball and 

 socket ; and the naviculare moves In several directions in turn- 

 inor the toes inwards, or in raising or depressing either side of 

 the foot, though the motions are greatly restrained by the liga- 

 ments which connect this to the other bones of the tarsus. 



Os Cuboides is an irregular cube. Behind, it is formed into 

 an oblong unequal cavity, adapted to the forepart of the os 

 calcis. On its internal side, there is a small semicircular smooth 

 cavity, to join the os naviculare. Immediately before which, 

 an oblong smooth plane is made by the os cuneifonnc exter- 

 num ; below this the bone is hollow and rough. On the internal 

 side of the lower surface, a round protuberance and fossa are 

 found, where the musculus abductor pollicis has its origin. On 

 the external side of this surface, there is a broad ridge running 

 forwards and inwards, covered with cartilage; immediately 

 before which a smooth fossa may be observed, in which the 

 tendon of the peroneus primus runs obliquely across the foot. 

 Before, the surface of the os cuboides is flat, smooth, and 

 slightly divided into two planes, for sustaining the os metatarsi 

 of the little toe, and of the toe next to it. 



The form of the back part of the os cuboides, and the liga- 

 ments connecting the joint with the os calcis, both concur in 

 allowing little motion in this part. 



Os cuneiforme externum is shaped like a wedge, being 

 broad and flat above, with long sides running obliquely down- 

 wards, and terminating in an edge. The upper surface of this 

 bone is an oblong square. The one behind is nearly a triangle, 

 but not complete at the inferior angle, and is joined to the os 

 naviculare. The external side is an oblong square divided as 

 it were by a diagonal ; the upper half of it is smooth, for its 

 conjunction with the os cuboides : the other is a scabrous hol- 

 low, with a small smooth impression made by the os metatarsi 

 of the toe next to the little one. The internal side of this bone 

 is flattened before by the metatarsal bone of the toe next to the 

 great one, and the back part is also flat and smooth where the os 

 cuneiforme medium is contiguous to it. The forepart of this bone 

 is triangular, for sustaining the os metatarsi of the middle toe. 



