286 OUTLINES OF EQUINE ANATOMY. 



with fibro- cartilage, fonning the anterior boundary of the 

 navicular joint, and affording the perforans tendon a sur- 

 face to play over. Its superior margin is straight, its 

 inferior convex. It presents two level surfaces sloping 

 slightly towards the centre, and thus rendering more pro- 

 minent a ridge which here extends from above downwards 

 across the surface. The inferior margin of the bone is 

 convex, and posteriorly is rough, with numerous foramina, 

 affording attachment to the inferior broad ligament (run- 

 ning from this to the postero-inferior surface of os pedis) ; 

 anteriorly it presents a smooth articulatory surface, elon- 

 gated from side to side, which moves arthrodially on a 

 corresponding surface of os pedis, and is continuous by 

 a smooth rounded edge with the iqji^er or anterior surface 

 of the bone. This is covered with articular cartilage, 

 articulating with os coronae ; it has two elongated concave 

 surfaces, which centrally are separated by a broad con- 

 vexity. Its superior margin is straight, its inferior convex. 

 The surfaces and margins culminate in the two extremities, 

 which are angles, with a slight inclination in a posterior 

 direction. To them are attached the stellate navicular 

 ligaments, each of which, attached here by a single head, 

 divides into three parts, one of which runs to the inner 

 part of the wing of os pedis, blending with the inferior 

 broad ligament, another runs to inner surface of the lateral 

 cartilage, while the third, after uniting with the terminal 

 expansion of the perforans tendon, passes upwards and 

 divides, one part, after becoming attached to the inner 

 surface of the sujjerior part of the lateral cartilage being 

 continued on to blend with the lateral ligament of the 

 pastern- joint, while the other runs direct to the middle 

 of the lateral surface of os suffraginis, where it is 

 attached. 



We have now examined the articulatory surfaces which 

 enter into the formation of the coffin and navicular joints. 

 The synovial membrane of the former covers the inner 

 surface of part of extensor pedis tendon and of the lateral 

 ligaments, and covers the anterior surface of both the broad 

 navicular ligaments. We have here a peculiar, but not 

 exceptional, union of a ginglymoid with an arthrodial 

 joint. The arrangement of the tendinous structure around 

 prevents the necessity for a capsular ligament. The syno- 

 vial membrane of the navicular joint (or more correctly 



