The Metacarpus consists of five bones; they are all long bones, with a shaft and two extremities. The shafts are constricted in the middle and curved so that they are slightly convex backwards; the carpal ends or bases of all, except the first, are more or less wedge-shaped, and the heads of all are rounded.

The first metacarpal is the shortest and stoutest of the five and has a saddle-shaped base for articulation with the trapezium. It supports only two phalanges.

Fig. 5. - Bones of the Right Hand (Anterior View).

The second metacarpal is the longest, and the other three gradually decrease in length. They articulate with one another at their carpal ends, and with the trapezoid, os magnum, and unciform in order. Each of the four inner metacarpals supports three phalanges.

The third metacarpal has a styloid process from its base on the radial side.

Ossification

The four inner metacarpals have a primary centre for the shafts and bases developed before birth,and the heads form a secondary epiphysis. The first metacarpal has the head and shaft formed from the primary centre and the base from the secondary centre.