Trapezoid

The trapezoid bone (lesser multangular bone) is a carpal bone in tetrapods, including humans. It is the smallest bone in the distal row. It may be known by its wedge-shaped form, the broad end of the wedge constituting the dorsal, the narrow end the palmar surface; and by its having four articular facets touching each other, and separated by sharp edges. It is homologous with the "second distal carpal" of reptiles and amphibians. Surfaces The superior surface, quadrilateral, smooth, and slightly concave, articulates with the scaphoid. The inferior surface articulates with the proximal end of the second metacarpal bone; it is convex from side to side, concave from before backward and subdivided by an elevated ridge into two unequal facets. The dorsal and palmar surfaces are rough for the attachment of ligaments, the former being the larger of the two. The lateral surface, convex and smooth, articulates with the trapezium. The medial surface is concave and smooth in front, for articulation with the capitate; rough behind, for the attachment of an interosseous ligament.

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