OSTEOLOCJY OF THE HORSE. 55 



perficies of the cylinder. — Tlie posterior surface is flattened, and, 

 in places, depressed. About one-third of its length down, it is 

 pierced by the medullary foramen, directed inward and downward. 

 Its sides present two triangular slips of rough scabrous surface, 

 extending about half way down, marking the places of attach- 

 ment of the small metacarpal bones. 



The superior extremity presents an articulatory surface, the 

 whole of which is flat, with the exception of a part bevelled off 

 on its outer side, which articulates with the unciform bone ; and 

 a small, depressed, bevelled spot on its inner and posterior side, 

 which receives part of the trapezoid bone : the flat surface sup- 

 ports the OS magnum, to which in figure it corresponds. It front, 

 and rather inclined to its inner side, the extremity has a roughen- 

 ed prominence, into which is implanted the extensor metacarpi : 

 on either side, the bone is asperated by the insertion of lateral li- 

 gaments ; and the rough part posteriorly gives origin to the sus- 

 pensory ligament. 



The iuferior extremity exhibits an articulatory trochlea, consist- 

 ing of two equal condyloid surfaces, parted by a semicircular emi- 

 nence, which is fitted into a counterpart formation in the upper 

 end of the large pastern bone. These condyles have uneven pits 

 in their sides, into which are fixed the lateral ligaments. 



Connexion — Superiorly, with the magnum, unciform, and tra- 

 pezoid bones ; laterally and posteriorly, with (he small metacarpal 

 bones ; inferiorly, with the large pastern and sesamoid bones. 



SxMALl, METACARPAL OR SPLINT BONES. 

 (OSSA METACARPI PARVA.) 



Number — Two :~ external and internal. Form. — Elongated; 

 pyramidal. 



Situation — Attached to the lateral and posterior parts of the 

 large metacarpal bone. 



Division — Into bases, middles, and apices. 



Extent — They vary somewhat in length : they commonly reach 

 about two-thirds of the large bone, downwards. 



The base, or head, is turned upwards, and is surmounted by a 

 flat articulatory surface, which enters into the formation of the 

 knee-joint. Below this, the bone is tuberous and rough, for liga- 

 mentous attachment: the external head also receives one of the 

 tendons of the flexor metacarpi externus ; the internal receives the 

 tendon of the flexor metacarpi internus. 



2'he middle is trifacial. The anterior surface is asperous, for 

 firm attachment to the large bone ; theinner surface is excavated, 

 to make room for the suspensory ligament ; the outer surface is 



