Editing Metacarpal bones (section)

==Structure==
[[File:Metacarpus (left hand) dorsal view.png|thumb|300px|Left hand shown with thumb on left.]]
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 is somewhat more mobile while the fifth metacarpal is semi-independent.<ref name="Tubiana-11">Tubiana ''et al'' 1998, p 11</ref>

Each metacarpal bone consists of a body or shaft, and two extremities; the ''head'' at the distal or digital end (near the fingers), and the ''base'' at the proximal or carpal end (close to the wrist).

=== Body ===
The ''body'' (''shaft'') is [[Prismatoid|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 [[interosseus muscle]]s, 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 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 ''[[Dorsal interossei of the hand|interossei dorsales]]''.
* To the tubercles on the digital extremities are attached the collateral ligaments of the [[metacarpophalangeal joints]].<ref name="Gray's">''[[Gray's Anatomy]]''. (See infobox)</ref>

=== Base ===
The ''base'' (''basis'') or ''carpal extremity'' is of a cuboidal form, and broader behind than in front. It articulates with the [[carpal bones]] and with the adjoining metacarpal bones while its dorsal and volar surfaces are rough, for the attachment of [[ligament]]s.<ref name="Gray's" />

=== Head ===
The ''head'' (''caput'') or ''digital extremity'' 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 muscle]]s.

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.<ref name="Gray's" />

=== Neck===
The neck, or ''subcapital'' segment, is the transition zone between the body and the head.

=== Articulations ===
Besides the [[metacarpophalangeal joint]]s, the metacarpal bones [[joint|articulate]] by [[carpometacarpal joint]]s as follows:
# the [[First metacarpal bone|first]] with the [[trapezium (bone)|trapezium]];
# the [[Second metacarpal bone|second]] with the trapezium, [[Trapezoid bone|trapezoid]], [[capitate]] and third metacarpal;
# the [[Third metacarpal bone|third]] with the capitate and second and fourth metacarpals;
# the [[Fourth metacarpal bone|fourth]] with the capitate, [[hamate]], and third and fifth metacarpals;
# and the [[Fifth metacarpal bone|fifth]] with the hamate and fourth metacarpal;
<gallery mode=packed heights=300px>
 File:Carpus.jpg|[[Carpometacarpal joints]] of the left hand. Thumb on left.
 File:Ospoignet.gif|Carpometacarpal joints of the left hand. Thumb on left.
 File:814 Radiograph of Hand.jpg|X-ray
</gallery>

=== Insertions ===
''[[Extensor Carpi Radialis Longus]]/[[Extensor Carpi Radialis Brevis|Brevis]]'': Both insert on the base of metacarpal II; Assist with wrist extension and radial flexion of the wrist

''[[Extensor Carpi Ulnaris]]'': Inserts on the base of metacarpal V; Extends and fixes wrist when digits are being flexed; assists with ulnar flexion of wrist

''[[Abductor Pollicis Longus]]'': Inserts on the trapezium and base of metacarpal I; Abducts thumb in frontal plane; extends thumb at carpometacarpal joint

''[[Opponens pollicis muscle|Opponens Pollicis]]'': Inserts on metacarpal I; flexes metacarpal I to oppose the thumb to the fingertips

''[[Opponens digiti minimi]]'': Inserts on the medial surface of metacarpal V; Flexes metacarpal V at carpometacarpal joint when little finger is moved into opposition with tip of thumb; deepens palm of hand.<ref>Saladin, Kenneth S. "Capt. 10." Anatomy & Physiology: the Unity of Form and Function. Dubuque: McGraw-Hill, 2010. 361-64. Print.</ref>
<gallery>
 File:Gray219 - Metacarpus.png|Metacarpus (yellow). Insertions are shown in red. Left hand, anterior (palmar) view. 
 File:Gray220 - Metacarpus.png|Metacarpus (yellow). Insertions are shown in red. Left hand, posterior (dorsal) view.
</gallery>