33 



THE OS CORON/E. 



This bone belongs to the class of long bones. It possesses 

 the peculiarities of having no medullary canal, and of being 

 more broad than long. In a horse of medium size it is about 

 an inch and a half in length, and two inches in width. Its 

 general form is cuboid. It articulates superiorly with the os 

 suffraginis or large pastern bone ; inferiorly with the os pedis 

 and navicular bone. Its anterior surface is rounded, its pos- 

 terior, flattened. 



It lies partly within and partly without the hoof. 



The tendon of the Flexor Pedis Perforatus is inserted into 

 its upper posterior border, and a little below its insertion is a 

 transverse flattened eminence covered by fibro-cartilage which 

 forms a gliding surface for the tendon of the Perforans. 



In blocky, upright feet, this bone is peculiarly subject to the 

 >3ti3 -affection known as Ring-bone. It is so short and firmly 

 braced to its position that it rarely becomes dislocated, but is 

 not quite so rarely the subject of fracture. 



OS NAVICULARE. 



SYNONYMS — Navicular _Bone — Shuttle Bone. 



This bone in its natural position, lies transversely between 

 the wings of the coffin-bone. It averages about two inches in 

 length ; half an inch in breadth ; and three eighths of an inch 

 at its thickest part. It has three surfaces of articulation, the 

 smallest with the coffin bone, the largest with the perforans 

 tendon and the medial sized one with the small pastern. It 

 is held in position by remarkably strong ligaments, and are 

 respectively named the interosseus ligament uniting it inferiorly 

 with the coffin bone ; two anterior, and two posterolateral, 

 that unite it with the small pastern. Besides these, from either 

 end of the bone proceed three ligaments. As they radiate 

 from the end of the bone as from a central point, they are 

 called the Stellate ligaments. 



The insertions of these ligaments embrace about half a circle, 

 the middle ligament going straight from the end of the bone 



