trapezoid bone

The trapezoid bone (lesser multangular bone) is a carpal bone in tetrapods, including humans.

The medial surface presents two facets; the upper, large and concave, articulates with the trapezoid bone; the lower, small and oval, with the base of the second metacarpal.

The lunate carpal bone straddles distally the bordering ulna and radius bones and proximally to distal carpus (wrist) Trapezium bone and Trapezoid bone.

In humans and our closest relatives the African apes (chimpanzees and gorillas) it fuses to the scaphoid where it forms the articulation with the trapezoid bone; occasionally it stays separate.