56 OSTEOLOGY OF THE HORSE. 



smooth and rounded. This part is terminated by a sharp edge 

 posteriorly. 



The apex is tapering and ends in a small bony tubercle, which 

 inclines backwards, away from the large bone. 



Difference — The external is commonly rather larger than the 

 internal bone ; they are, however, with more certainty distin- 

 guished by their articulatory surfaces. 



Connexion — The external bone supports the unciform; the in- 

 ternal, the trapezoid : both are attached to the large metacarpal 

 bone. 



Development — In the growing animal the splint bones are 

 maintained by cartilago-ligamentous connexions : in most adult, 

 and in all old subjects, the ligamentous substance becomes con- 

 verted into osseous matter. 



OF THE PASTERN. 

 The pastern, corresponding to the first phalanx of the human 

 foot, is supported by the pastern bone ; but it has also two ap- 

 pendices, the sesamoid bones, which are necessary to the forma- 

 tion of the fetlock -joint. 



PASTERN BONE. (OS S U FFR AGl N IS .) 



Situation — Below the cannon bone, with which, from taking 

 an oblique direction, it forms an obtuse angle. 



Form — Cylindroid, flattened before and behind ; larger supe- 

 riorly than inferiorly : about one-third the length of the cannon 

 bone. 



Division — Into body, and superior and inferior extremities. 



The body presents two surfaces. The anterior is even and 

 convex : the posterior is uneven, but flattened, and displays a 

 slightly depressed triangular portion, into the asperous angle of 

 which is implanted the short sesamoid ligament. 



The superior or larger extremity/ consists of two shallow ar- 

 ticular cups, laterally, with a deeper transverse articular groove 

 running between them, in which play the condyles and middle 

 eminence of the lower extremity of the cannon bone. Behind, at 

 the sides of the cups, are two tuberosities, to which are fixed the 

 crucial ligaments. 



The inferior extremity is bi-convex or condyloid ; consisting of 

 two equal, articular, semi-cylindroid convexities, parted by a 

 transverse shallow depression, running from before backward, but 

 more completely separated by a little pit behind. The asperous 

 prominences on the sides are for ligamentous attachment. 



Connexion — With the cannon and coronet bones, and with the 

 two sesamoids. 



