The =radial carpal= bone (Os carpi radiale, scaphoid) is the largest
bone of the upper row; it is somewhat compressed laterally, and is
clearly six-sided. The =superior= or =proximal surface= is convex in
front, concave behind, and articulates with the inner facet on the
distal end of the radius. The =inferior= or =distal surface= is also
convex in front and concave behind; it articulates with the second and
third carpal bones. The =external 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 =anterior= or =dorsal
surface= is rough and slightly convex. The =internal surface= and the
=posterior= or =volar surface= are rough and tuberculate.
[Illustration:
FIG. 51.—SAGITTAL SECTION OF UPPER PART OF RADIUS AND ULNA OF HORSE.
_Cm_, Medullary cavity of ulna.
]