96 



THE SKELETON OF THE HORSE 



three facets for articulation with the third carpal bone. The dorsal and 

 medial surfaces are continuous and bear a tuberosity to which the collateral liga- 

 ment is attached. The distal surface is articular and consists of a large flattened 

 facet for the second or inner metacarpal bone, and a small one for the third or large 

 metacarpal bone. Some specimens have a small facet on the lower part of the volar 

 surface which articulates with the first carpal bone. 



Ca 



/ 





li.- 



The Third Carpal Bone 



The third carpal bone (Os carpale tertium)i is much the largest bone of the 



distal row, forming more than 

 two-thirds of the width of the 

 latter. It is flattened from 

 above downward, and is twice as 

 ■ndde in front as behind. The 

 proximal surface consists of two 

 facets separated by an antero-pos- 

 terior ridge; the medial facet is 

 concave and articulates with the 

 radial carpal; the lateral facet — 

 for the intermediate carpal — is 

 concave in front and convex be- 

 hind, where it encroaches on the 

 volar surface. The distal surface 

 is slightly undulating, and articu- 

 lates almost entirely with the third 

 or large metacarpal bone, but it 

 usually bears a small oblique facet 

 at its medial side for the second 

 metacarpal, and there is commonly 

 a non-articular depression later- 

 ally. The medial surface faces 

 backward and inward, and bears 

 three facets for articulation with 

 the second carpal, between which 

 it is excavated and rough. The 

 lateral surface has two facets for 

 articulation with the fourth car- 

 pal, and is depressed and rough 

 in its middle. The dorsal sur- 

 face is convex and is crossed 

 by a rough transverse ridge. The 

 volar surface is relatively small, 

 and is rounded; its upper part 



Cr 



C2 



CI 



McII 



McIII 



Fig. 72. — Left Carpus of Horse, with Parts of Adjacent 

 Bones; Medial View. 

 Cr, Radial carpal; Ca, accessory carpal; CI, first carpal; 

 CS, second carpal; McII, McIII, metacarpal bones; 1, tuber- 

 osity of radius for attachment of medial ligament of carpus; 

 2, groove for tendon of extensor carpi obliquus; 3, third car- 

 pal; 4, metacarpal tuberosity. 



is encroached upon by the proximal articular surface, below which it is ]*6ugh. 



The Fourth Carpal Bone 



The fourth carpal bone (Os carpale quartum)^ is somewhat wedge-shaped, and 

 is readily distinguished from the second by its greater size and its volar tubercle. 

 The proximal surface articulates with the intermediate and ulnar; it is convex and 

 curves outward, l)ackward, and downward, encroaching on the lateral and volar sur- 

 faces. The distal surface bears two medial facets for the third or large metacarpal 



1 Also known as the os magnum or capitatum. 

 ^ Also known as the unciform or hamatum. 



