THE ANTERIOR LIMBS. 



81 



with the r semilunar and scaphoides ; below, with the principal metacarpal 

 and the internal rudimentary metacarpal. 



The third, or trapezoides, the smallest, is provided with five facets, and 

 is in contact with the scaphoides above, and the middle and internal meta- 

 carpals below. 



Collectively, these bones of the lower row form two Fig- 47. 



large diarthrodial surfaces. The upper surface responds 

 to the bones of the upper row, and is constituted in front, 

 and from without to within, by a small condyle and two 

 glenoid cavities; behind, by two isolated condyles, 

 formed by the os magnum and the trapezoides. The 

 inferior articular surface is only formed by more or less 

 long and plane facets, which incline towards each other. 

 It corresponds to the three portions of the metacarpus. 



Structure and development. Each carpal bone is 

 formed by a nucleus of close spongy substance enveloped 

 in a layer of compact tissue. Each is developed from 

 a single centre of ossification. 



2. Metacarpal Bones. 



In Solipeds, the metacarpus is composed of three 

 bones, named the " metacarpals/' standing parallel to each 

 other. These are the principal metacarpal and the two 

 rudimentary metacarpals, an external and internal, 



PRINCIPAL METACARPAL. This is a long cylindrical 

 bone, situated vertically between the carpus and the 

 digital region. 



Body. The body is a little depressed before and 

 behind, a disposition which permits it to be described 

 as "having livo faces and two borders. The anterior face 

 is perfectly smooth and rounded from side to side. The 

 posterior face is flat, and exhibits: 1, Towards the upper 

 third, the nutritive foramen of the bone; 2, On the 

 sides, two narrow, roughened surfaces, parallel and elon- 

 gated vertically, commencing near the superior extremity 

 to disappear a little below the middle of the bone ; these 

 surfaces are held in apposition with the rudimentary 

 metacarpals by means of an interosseous ligament which 

 is often ossified in old horses. The borders, external and 

 internal, are very thick, round, and smooth, like the an- 

 terior face. 



Extremities. The superior is flattened before and 

 behind, and presents : 1, Above, an undulating articu- 

 latory surface, formed by the union of several flat 

 facets more or less inclined on one another : they 

 respond to all the lower row of carpal bones ; 2, An- 

 teriorly and inwardly, a tuberosity for muscular inser- 

 tion ; 3, Posteriorly, and directly above the roughened 

 surfaces of the posterior face, four small diarthrodial facets in pairs, and 

 running into the larger articular surface by their superior border : they are 

 adapted to similar facets on the rudimentary metacarpals. The inferior 

 extremity, elongated transversely, corresponds to the first phalanx and the 

 large sesamoids by an articular surface, convex from before to behind, which 



POSTERIOR VIEW OF 

 RIGHT METACARPUS. 



1, Head of large meta- 

 carpal bone for ar- 

 ticulation with the 

 trapezoides, mag- 

 num, and unciform ; 

 2, Inner splint, or 

 small metacarpal 

 bone, for articula- 

 tion with the trape- 

 zoides ; 4, Scabrous 

 surface for the at- 

 tachment of the sus- 

 pensory ligament ; 

 5, Nutrient fora- 

 men ; 6, Median 

 ridge separating the 

 two inferior con- 

 dyles. 



