The =ulnar carpal= bone (Os carpi ulnare, cuneiform) is the smallest and
most irregular bone of the upper row. The =superior= or =proximal
surface= is concave, and fits the lower part of the outer facet on the
distal end of the radius. The =inferior= or =distal surface= is oblique
and undulating for articulation with the fourth carpal bone. The
=internal surface= has upper and lower facets for articulation with the
intermediate. The =anterior= or =dorsal= and =external surfaces= are
continuous, convex, and rough. The =posterior= or =volar surface= is
oblique, and bears a concave facet for articulation with the accessory
carpal bone; below this is a tubercle.
[Illustration:
FIG. 52.—LEFT CARPAL BONES OF HORSE, WITH DISTAL END OF RADIUS AND
PROXIMAL END OF METACARPUS; INTERNAL VIEW.
]
[Illustration:
FIG. 53.—LEFT CARPAL BONES OF HORSE, WITH ADJACENT ENDS OF RADIUS AND
METACARPUS; EXTERNAL VIEW.
_Ca_, Accessory carpal bone; _Cr_, radial carpal; _Ci_, intermediate
carpal; _Cu_, ulnar carpal; _C1–4_, first to fourth carpals; _Mc.
II_, _III_, _IV_, metacarpal bones; _1_, groove for tendon of
extensor carpi obliquus; _2_, groove for lateral extensor tendon;
_3_, groove for tendon of flexor carpi externus; _4_, metacarpal
tuberosity. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]