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In human anatomy, the metacarpus is the intermediate part of the hand skeleton that is located between the phalanges (bones of the fingers) distally and the carpus which forms the connection to the forearm. The metacarpus consists of metacarpal bones. Its equivalent in the foot is the metatarsus.
The metacarpals form a transverse arch to which the rigid row of distal carpal bones are fixed. The peripheral metacarpals (those of the thumb and little finger) form the sides of the cup of the palmar gutter and as they are brought together they deepen this concavity. The index metacarpal is the most firmly fixed, while the thumb metacarpal articulates with the trapezium and acts independently from the others. The middle metacarpals are tightly united to the carpus by intrinsic interlocking bone elements at their bases. The ring metacarpal forms a transitional element of the semi-independent last metacarpal.
Each consists of a body and two extremities.
The body (corpus; shaft) is prismoid in form, and curved, so as to be convex in the longitudinal direction behind, concave in front.
It presents three surfaces: medial, lateral, and dorsal.
To the tubercles on the digital extremities are attached the collateral ligaments of the metacarpophalangeal joints.
The base or carpal extremity (basis) is of a cuboidal form, and broader behind than in front: it articulates with the carpus, and with the adjoining metacarpal bones; its dorsal and volar surfaces are rough, for the attachment of ligaments.
The head or digital extremity (capitulum) presents an oblong surface markedly convex from before backward, less so transversely, and flattened from side to side; it articulates with the proximal phalanx.
It is broader, and extends farther upward, on the volar than on the dorsal aspect, and is longer in the antero-posterior than in the transverse diameter.
On either side of the head is a tubercle for the attachment of the collateral ligament of the metacarpophalangeal joint.
The dorsal surface, broad and flat, supports the tendons of the extensor muscles; the volar surface is grooved in the middle line for the passage of the Flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface.
Besides their phalangeal articulations, the metacarpal bones articulate as follows:
The fourth and fifth metacarpal bones are commonly “blunted,” or shortened, in pseudohypoparathyroidism and pseudopseudohypoparathyroidism.
A blunted fourth metacarpal, with normal fifth metacarpal, can signify Turner syndrome.
In four-legged animals, the metacarpals form part of the forefeet, and are frequently reduced in number, appropriate to the number of toes. In digitigrade and unguligrade animals, the metacarpals are greatly extended and strengthened, forming an additional segment to the limb, a feature that typically enhances the animal’s speed. In both birds and bats, the metacarpals form part of the wing.
This article was originally based on an entry from a public domain edition of Gray’s Anatomy. As such, some of the information contained within it may be outdated.