80 OUTLINES OF EQUINE ANATOMY. 



aTticulatory facet to blend witli that of tlie large bone, 

 wbicb articulates with os magnum, while postero-externally 

 is a small facet for connection with os pisiforme. It gives 

 attachment to extensor metacarpi obliquus and flexores 

 nietacarpi internus and medius, the latter through the 

 medium of the annular ligament of the knee. To it also 

 is attached the inner lateral ligament of that joint. It is 

 larger and longer than the outer small bone. 



The outer small metacarjxil hone supero-externally is 

 rough for attachment of the outer lateral, and the annular 

 ligament of the knee, also of flexor metacarpi externus. 

 Supero-internally it presents an articulatory surface, flat 

 and slanting inwards, on which os unciforme glides. 



SESAMOID BONES, two in number in each limb, are 

 situated at the fetlock behind the inferior extremity of the 

 large metacarpal bone on which they play, f .)r their anterior 

 surfaces are articulatory, and they are so united together 

 that the surfaces of the two bones form the counterpart 

 of the posterior part of the inferior extremity of the large 

 metacarpal bone. Each bone presents four surfaces. The 

 anterior surface is triangular and articulatory, consists ex- 

 ternally of a large smooth surface, which inwardly becomes 

 reflected backwards in forming with its fellow the counter- 

 part of the central ridge of the inferior extremity of the 

 large metacarpal bone. This surface inwardly is connected 

 by the inner margin to \\iq ]josterior surface. This margin 

 gives attachment to the intersesamoid ligament which 

 binds the bones together, and thus renders their posterior 

 surfaces which are coated with fibro-cartilage, a convenient 

 groove for the flexor tendons to play over. The inferior 

 surface is rough, triangular, and presents foramina ; from 

 it the inferior sesamoid ligaments extend. The outer sur- 

 face inclines obliquely upwards and inwards in such a 

 manner as to form a point superiorly in meeting the anterior 

 and posterior surfaces. The posterior margin of this sur- 

 face presents a prominent ridge, and anteriorly some large 

 foramina. From the ridge the lateral sessamoid ligaments 

 run, and also to the ridge are attached those portions of 

 the superior sesamoideal ligament which pass to extensor 

 pedis, and also the annular ligaments of the fetlock. 



OS SDEFRAGINIS is the long roimd bone which extends 

 from the fetlock to the pastern joint. Its shaft is short and 

 slightly compressed from before backwards. The anterior 



