94 OUTLINES OF EQUINE ANATOMY. 



posterior surface of the tubercle. More outwardly, sepa- 

 rated from tlie ridge by a deep perforated fossa, is an 

 ovoid articulately surface for os calcis, extending directly 

 downwards ; and more outwards, inclined to the outer sur- 

 face and extending obliquely forwards, is an articulatory 

 facet consisting of two parts, one of wbicb is vertical, the 

 other horizontal. A little lower down, on the outer side, is 

 another small facet, elongated from above downwards. We 

 see a third at the inf ero-external angle of the bone con- 

 tinuous with that on the inferior surface of the bone. The 

 interarticular space is rough and perforated. The outer sur- 

 face is small, rough, and concave, giving attachment to one of 

 the lateral ligaments. The inner surface is roughened and 

 flat superiorly, inferiorly forms a prominent tubercle ; to- 

 the whole of it ligamentous substance is attached. The an- 

 terior margm of both the inner and outer surfaces is occupied 

 by the outer margin of the supero- anterior articular ridges. 

 The inferior surface is mainly articulatory, consisting of a 

 slightly convex surface, elongated from side to side, ex- 

 ternally continuous with a small triangular facet for os 

 cuboides, which is continuous with one on the posterior 

 part for os calcis. Anteriorly it almost reaches the internal 

 ridge, and at the under surface of the tubercle is reflected 

 backwards, extending to about the centre of the posterior 

 part of the bone, where it terminates in becoming continu- 

 ous with the inner articulatory facet for os calcis of the 

 posterior part. The anterior and reflected portions are 

 separated by a gap in the articular cartilage, which presents 

 numerous foramina. This portion internally is more con- 

 cave than the rest of the surface, being separated from its 

 outer extremity by a prominent point. This large articu- 

 latory surface comes in apposition with cuneif orme magnum. 

 OS CUNEIFORME MAGNUM is a flat bone with two 

 surfaces and four margins. The sujyerior surface is concave 

 in most parts, and is prominent at the outer j^art of its 

 anterior margin. It is the exact counterpart of the infe- 

 rior extremity of astragalus (with exception of its small 

 surface for os cuboides), and therefore requires no detailed 

 description. Its posterior part is most prominent, espe- 

 cially inwardly ; inferiorly it articulates with ossa cunei- 

 forme parvum and medium. For medium it presents a 

 large articulatory surface, extending along the anterior 

 border, having a convex anterior, concave posterior margin 



