In humans and other primates, any of the
five long, cylindrical bones in the region of the palm of the hand.
The metacarpals, known collectively as the metacarpus, run from the base
of the wrist, where they articulate with the carpals (wrist bones), to the base of each finger, where they articulate with
the phalanges (finger bones). On the palm,
the metacarpals are covered by a thick layer of fascia (fibrous connective tissue); on the back of the hand, the metacarpals can
be seen and felt through the skin. The heads of the metacarpals form the
In four-footed animals, the metacarpals are the bones of the forefoot. The
number of metacarpals varies between species. In the pentadactyl limb (which
has five digits) there are five, but this number is reduced in many species.
Osteology of the metacarpals (Gray's Anatomy,
The metacarpus consists of five cylindrical bones which are numbered from
the lateral side (ossa metacarpalia I-V); each consists of a body
and two extremities.
Common characteristics of the metacarpal
The body (corpus; shaft)
The body 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. The medial and lateral surfaces are concave, for the
attachment of the Interossei, and separated from one another by a prominent
anterior ridge. The dorsal surface presents in its distal two-thirds a smooth,
triangular, flattened area which is covered in the fresh state, by the tendons
of the extensor muscles. This surface is
bounded by two lines, which commence in small tubercles situated on either
side of the digital extremity, and, passing upward, converge and meet some
distance above the center of the bone and form a ridge which runs along
the rest of the dorsal surface to the carpal extremity. This ridge separates
two sloping surfaces for the attachment of the Interossei dorsales. To the
tubercles on the digital extremities are attached the collateral ligaments
of the metacarpophalangeal joints.
The base or carpal
The base 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)
The head 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 Extensor tendons; 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.
Characteristics of the
individual metacarpal bones
|The first metacarpal bone (os metacarpale I; metacarpal
bone of the thumb)
This is shorter and stouter than the others, diverges to a greater
degree from the carpus, and its volar surface is directed toward the
palm. The body is flattened and broad on its dorsal surface, and does
not present the ridge which is found on the other metacarpal bones;
its volar surface is concave from above downward. On its radial border
is inserted the Opponens pollicis; its ulnar border gives origin to
the lateral head of the first Interosseus dorsalis.
The base presents a concavo-convex surface, for articulation with
the greater multangular; it has no facets on its sides, but on its
radial side is a tubercle for the insertion of the Abductor pollicis
longus. The head is less convex than those of the other metacarpal
bones, and is broader from side to side than from before backward.
On its volar surface are two articular eminences, of which the lateral
is the larger, for the two sesamoid
bones in the tendons of the Flexor pollicis brevis.
|The second metacarpal bone (os metacarpale II; metacarpal
bone of the index finger)
This is the longest, and its base the largest, of the four remaining
bones. Its base is prolonged upward and medialward, forming a prominent
ridge. It presents four articular facets: three on the upper surface
and one on the ulnar side. Of the facets on the upper surface the
intermediate is the largest and is concave from side to side, convex
from before backward for articulation with the lesser multangular;
the lateral is small, flat and oval for articulation with the greater
multangular; the medial, on the summit of the ridge, is long and narrow
for articulation with the capitate. The facet on the ulnar side articulates
with the third metacarpal. The Extensor carpi radialis longus is inserted
on the dorsal surface and the Flexor carpi radialis on the volar surface
of the base.
|The third metacarpal bone (os metacarpale III; metacarpal
bone of the middle finger)
This is a little smaller than the second. The dorsal aspect of its
base presents on its radial side a pyramidal eminence, the styloid
process, which extends upward behind the capitate; immediately distal
to this is a rough surface for the attachment of the Extensor carpi
radialis brevis. The carpal articular facet is concave behind, flat
in front, and articulates with the capitate. On the radial side is
a smooth, concave facet for articulation with the second metacarpal,
and on the ulnar side two small oval facets for the fourth metacarpal.
|The fourth metacarpal bone (os metacarpale IV; metacarpal
bone of the ring finger)
This is shorter and smaller than the third. The base is small and
quadrilateral; its superior surface presents two facets, a large one
medially for articulation with the hamate, and a small one laterally
for the capitate. On the radial side are two oval facets, for articulation
with the third metacarpal; and on the ulnar side a single concave
facet, for the fifth metacarpal.
|The fifth metacarpal bone (os metacarpale V; metacarpal
bone of the little finger)
This presents on its base one facet on its superior surface, which
is concavo-convex and articulates with the hamate, and one on its
radial side, which articulates with the fourth metacarpal. On its
ulnar side is a prominent tubercle for the insertion of the tendon
of the Extensor carpi ulnaris. The dorsal surface of the body is divided
by an oblique ridge, which extends from near the ulnar side of the
base to the radial side of the head. The lateral part of this surface
serves for the attachment of the fourth Interosseus dorsalis; the
medial part is smooth, triangular, and covered by the Extensor tendons
of the little finger.
Besides their phalangeal articulations, the metacarpal bones articulate
as follows: the first with the greater multangular; the second with the
greater multangular, lesser multangular, capitate and third metacarpal;
the third with the capitate and second and fourth metacarpals; the fourth
with the capitate, hamate, and third and fifth metacarpals; and the fifth
with the hamate and fourth metacarpal.