The peripheral metacarpals (those of the thumb and little finger) form the sides of the cup of the palmer gutter and when they are brought together they deepen this concavity. The index metacarpal is the most firmly fixed, while the thumb metacarpal articulates with the trapezium. It also acts independently from the other metacarpals. The metacarpals are what form the shape of the hand. Each metacarpal consists of a body and two extremities (head and base). The head of the metacarpals is what forms the hand’s knuckles along with the base of phalanges that connect with them. The middle metacarpals are tightly connected to the carpus by very intrinsic interlocking bone elements at their bases. The ring finger metacarpal forms a transitional element of the semi-independent last (baby finger) metacarpal.
The Body (corpus; shaft) is prismoid in shape, and curved, so as to be convex in the longitudinal direction behind, and concave (curved inward) in the front. It presents three surfaces which are the medial, the lateral, and the dorsal.
The medial (of,in, or toward the middle) and the lateral (at or toward the side of) surfaces are concave to allow for attachment of the interosseous muscles and these surfaces are each separated by a prominent, anterior ridge.
The dorsal (pertaining to the back) surface presents in its distal two-thirds a smooth, triangular, flattened area which is covered by the tendons of the extensor muscles.
The base or carpal extremity is of cuboidal form.
It is broader in the back than in the front.
The base articulates with the carpus.
The base articulates with the adjoining metacarpal bones.
Its’ dorsal and volar (of or pertaining to the palm of the hand) surfaces are rough to accommodate the attachment of the ligaments
The dorsal surface which is broad and flat supports the tendons of the extensor muscles.