56 THE SURGICAL ANATOMY OF THE HORSE 



Its superior articular surface presents facets which articulate with the 

 trapezoid, magnum, and unciform bones. Its inferior articular surface 

 presents two slightly convex areas separated by an antero-posterior ridge. 

 The ridge and the convex areas articulate inferiorly with the superior 

 surface of the long pastern bone or os suffraginis. The convexities and 

 the ridge extend upwards by encroaching upon the posterior aspect of 

 the bone, and this portion, which looks backwards, articulates with 

 the anterior surface ot the sesamoid bones. 



The anterior and lateral surfaces are for the most part smooth, 

 rounded from side to side, and blended with one another. The anterior 

 surface shows, near the upper extremity of the bone and towards the 

 inner side, a roughened area, which is slightly elevated, and 

 which gives insertion to the tendon of the extensor metacarpi magnus 

 muscle. The superior and inferior extremities of the lateral surfaces 

 are roughened for the attachment of the lateral ligaments of the knee 

 and fetlock. 



The posterior surface is almost flat, and it forms, with the small 

 metacarpal bones, a channel for the accommodation of the suspensory 

 ligament. Near its upper extremity this surface is roughened for the 

 attachment of the ligament just mentioned. On the posterior surface the 

 nutrient foramen is placed between the upper and middle thirds. Two 

 roughened areas are also found, one on either side of this surface. Each 

 is in the form of an elongated triangle, the apex of which is directed 

 downwards, and is situate about half-way down the bone, and the base 

 just below its upper extremity. To these areas the small metacarpal 

 or splint bones are articulated. Above each area are two small facets 

 which form synovial joints with like facets on the corresponding small 

 metacarpal. 



The lateral ligaments of the fetlock are attached to two roughened 

 depressions placed one on either side of the inferior extremity. 



The shaft and superior extremity ossify from the same centre, but 

 the distal extremity has a separate centre of ossification. 



