94 THE SKELETON OF THE HORSE 
(abbreviated) names and relative positions of the bones of the left carpus are in- 
dicated below: 
Proximal Row: 
— . . + — 
Ss Radial Intermediate Ulnar = Accessory | & 
c = 
= Distal Row: a 
| First Second Third Fourth 
THE RADIAL CARPAL BONE 
The radial carpal bone (Os carpi radiale)'is the largest bone of the proximal row; 
it is somewhat compressed transversely, and is clearly six-sided. The proximal 
surface is convex in front, concave behind, and articulates with the medial facet 
on the distal end of the radius. The distal surface is also convex in front and con- 
‘cave behind; it articulates with the second and third carpal bones. The lateral 
surface bears upper and lower facets on its anterior part for articulation with the 
intermediate; between and behind these it is excavated and rough. The dorsal 
surface is rough and slightly convex. The medial surface and the volar surface 
are rough and tuberculate. 
THE INTERMEDIATE CARPAL BONE 
The intermediate carpal bone (Os carpi intermedium)? is somewhat wedge- 
shaped, wider in front than behind. The proximal surface is saddle-shaped, and 
articulates with the middle facet on the distal end of the radius. The distal sur- 
face is smaller, convex in front, concave behind, and articulates with the third and 
fourth carpal bones. The medial surface has upper and lower facets for articula- 
tion with the radial carpal, and between these it is excavated and rough. 
The lateral surface is similar to the preceding and articulates with the ulnar car- 
pal. The dorsal surface is rough and slightly convex. The volar surface bears a 
tuberosity on its lower part. 
THE ULNAR CARPAL BONE 
The ulnar carpal bone (Os carpi ulnare)* is the smallest and most irregular 
bone of the proximal row. The proximal surface is concave and fits the lower part 
of the lateral facet on the distal end of the radius. The distal surface is oblique 
and undulating for articulation with the fourth carpal bone. The medial surface 
has upper and lower facets for articulation with the intermediate. The dorsal and 
lateral surfaces are continuous, convex, and rough. The volar surface is oblique, 
and bears a concave facet for articulation with the accessory carpal bone; below 
this is a tubercle. 
THE ACCESSORY CARPAL BONE 
The accessory carpal bone (Os carpi accessorium)* is situated behind the ulnar 
carpal bone and the lateral part of the distal end of the radius. It is discoid and pre- 
sents for description two surfaces and a circumference. The medial surface is con- 
cave and forms the lateral wall of the carpal groove. The lateral surface is con- 
vex and rough; a smooth groove for a tendon crosses its anterior part obliquely 
downward and slightly forward. The dorsal border bears two facets; the proximal 
one is concave and articulates with the back of the lateral facet on the distal end of 
the radius; the distal one is convex and articulates with the ulnar carpal bone. 
The remainder of the circumference is rounded and rough. 
1 Also known as the seaphoid. 2 Also known as the semilunar or lunar. 
3 Also known as the cuneiform. 
4 Also known as the pisiform and erroneously as the trapezium. 
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