98 THE SKELETON OF THE HORSE 
face is small, being encroached upon by the proximal articular surface. The volar 
surface bears a tubercle on its distal part." 
THE CARPUS AS A WHOLE 
The bones of the carpus, exclusive of the accessory, form an irregular quadran- 
gular mass, the width of which is about twice the height or the dorso-volar diameter. 
The dorsal surface is convex from side to side, depressed along the line of junction 
of the two rows, and prominent below. The volar surface is in general slightly 
convex, but very irregular. It forms with the accessory 
carpal the carpal groove (Sulcus carpi), which in the recent 
state is rendered smooth by the volar ligament; it is con- 
verted into the carpal canal (Canalis carpi) for the flexor 
tendons by the transverse carpal ligament, which stretches 
across from the accessory bone to the medial side. The 
proximal surface is widest medially and is elevated in front, 
coneave behind; it is entirely articular and adapted to the 
‘carpal articular surface of the radius. The distal surface 
is also articular and is irregularly faceted in adaptation to 
the surfaces of the metacarpal bones; each of the distal 
bones usually articulates with two metacarpal bones, but 
sometimes the third rests on the third metacarpal only. 
The medial and lateral surfaces are both irregular and 
rough, the former being the wider. With the exception of 
the accessory, ulnar, and second, each bone articulates 
with two bones of the other row. 
Development.— Each ossifies from a single center. 
MclV MclIlI Mell 
Fic. 76.—RicuTt METACARPAL Fic. 77.—ProxtMau Extremities oF Lerr MeracarpaL Bones oF Horse; END 
Bones OF Horse; VOLAR VIEW. 
VIEW. 2, 2’, Facets for second carpal bone; 3, 3’, facets for third carpal bone; 4, 4’, facets 
1, Nutrient foramen of for fourth carpal bone; 5, metacarpal tuberosity, 
large (third) metacarpal bone; 
2, 3, 4, proximal extremities; 5, 
surface for attachment of sus- THE METACARPUS 
pensory ligament; 6, sagittal 
ridge of distal end of large meta- Three metacarpal bones (Ossa metacarpalia) are 
carpal bone; 7, 7’, distal ends of : _ ees 
ener hess cstarencs °F present in the horse. Of these, only one, the third or 
small (second and fourth) meta- 3 5 . 7 S 
carpal bones. large metacarpal bone, is fully developed and carries a 
I 5 . 
digit; the other two, the second and fourth, are much 
reduced, and are commonly called the small metacarpal or ‘“‘splint”’ bones. 
THE THIRD OR LARGE METACARPAL BONE 
This (Os metacarpale tertium) is a very strong long bone, which is situated ver- 
ticaily between the carpus and the first phalanx. It consists of a shaft and two ex- 
tremities. 
1This bone is probably equivalent to the fourth and fifth carpals of forms in which five 
carpal elements are present in the distal row. 
