THE BONES OF THE TARSUS 67 



groove, the whole being for articulation with the inferior end of the 

 tibia. The surface presented is thus pulley-like, and it winds half-way- 

 round the bone with a direction which is forwards, downwards, and 

 outwards. 



The posterior surface is irregular, and presents three or four facets 

 for articulation with like facets on the anterior surface of the body of 

 the calcis. 



The inferior surface is slightly convex. It presents a large facet 

 for articulation with the superior surface of the scaphoid. For the rest 

 of its extent this surface is non-articular and roughened for the attach- 

 ment of the astragalo-scaphoid interosseous ligament. 



The external lateral surface is roughened, and presents a pit for the 

 attachment of one of the slips of the external lateral ligament of the 

 hock. The inner lateral surface is also roughened, and presents a well- 

 defined, prominent tubercle from which the astragalo-metatarsal liga- 

 ment arises. This tubercle forms a very important superficial landmark 

 in the living animal. The size of the tubercle varies considerably in 

 different animals, irrespective of the size of the animal, as also does 

 the size of the prominence caused by the internal malleolus of the 

 tibia, which is found just above that caused by the tubercle mentioned. 

 It is thus of considerable surgical importance to compare the pro- 

 minences on both hocks when subjecting them to examination. 



The Os Calcis. — This bone is made up of a body and a large process 

 termed the tuber calcis. Together with the astragalus, it forms what 

 may be called the upper row of tarsal bones. 



The body is very irregular in shape. Anteriorly it presents three 

 or four facets for articulation with the facets already described on the 

 back of the astragalus, whilst between them the bone is roughened for 

 the attachment of the calcaneo-astragaloid interosseous ligament. On 

 the inferior surface of the body is an elongated facet, which is slightly 

 concave, and which articulates with the cuboid. Superiorly and 

 towards its outer side the body is continued by the tuber, whilst the 



