The second metacarpal bone (metacarpal bone of the

index finger The index finger (also referred to as forefinger, first finger, second finger, pointer finger, trigger finger, digitus secundus, digitus II, and many other terms) is the second digit of a human hand. It is located between the thumb and the mi ...

) is the longest, and its base the largest, of all the

metacarpal bones In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...

.'' Gray's Anatomy'' (1918). See infobox.

Human anatomy

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

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

r 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 trapezoid bone (lesser multangular bone) is a carpal bone in tetrapods, including humans. It is the smallest bone in the distal row of carpal bones that give structure to the palm of the hand. It may be known by its wedge-shaped form, the bro ...

; ** the ''lateral'' is small, flat and oval for articulation with the

greater multangular The trapezium bone (greater multangular bone) is a carpal bone in the hand. It forms the radial border of the carpal tunnel. Structure The trapezium is distinguished by a deep groove on its anterior surface. It is situated at the radial side of ...

; ** the ''medial'', on the summit of the ridge, is long and narrow for articulation with the

capitate The capitate bone is a bone in the human wrist found in the center of the carpal bone region, located at the distal end of the radius and ulna bones. It articulates with the third metacarpal bone (the middle finger) and forms the third carpomet ...

. * The facet on the ulnar side articulates with the

third metacarpal The third metacarpal bone (metacarpal bone of the middle finger) 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; ...

. The extensor carpi radialis longus muscle is inserted on the dorsal surface and the

flexor carpi radialis muscle In anatomy, flexor carpi radialis is a muscle of the human forearm that acts to flex and (radially) abduct the hand. The Latin ''carpus'' means wrist; hence flexor carpi is a flexor of the wrist. Origin and insertion The flexor carpi radialis is ...

on the volar surface of the base. The shaft gives origin to the first palmar interosseus and the first and second dorsal interossei. This bone is often the most prone to damage from fast bowlers in

cricket Cricket is a bat-and-ball game played between two teams of eleven players on a field at the centre of which is a pitch with a wicket at each end, each comprising two bails balanced on three stumps. The batting side scores runs by st ...

, as it is furthest down the bat handle on both left- and right-handers, and as such is in danger of being struck by balls that are pitched short.Laven, Kate. "West Indies' Courtney Walsh still in love with cricket." Daily Telegraph ondon5 May 2009 Print.

Evolution

The articulation between the second metacarpal and the capitate is considered uniquely specialized in

hominid The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the e ...

s. On the second metacarpal, the facet for the capitate is directed proximally, almost perpendicular to the facet for the third metacarpal, while the corresponding facet on the capitate is oriented distally. This is to receive compressive forces generated by the pad-to-pad

opposition Opposition may refer to: Arts and media * ''Opposition'' (Altars EP), 2011 EP by Christian metalcore band Altars * The Opposition (band), a London post-punk band * '' The Opposition with Jordan Klepper'', a late-night television series on Com ...

between the thumb and the index finger. In contrast, in apes, including fossil apes such as ''

Dryopithecus ''Dryopithecus'' is a genus of extinct great apes from the middle–late Miocene boundary of Europe 12.5 to 11.1 million years ago (mya). Since its discovery in 1856, the genus has been subject to taxonomic turmoil, with numerous new species b ...

'' and ''

Proconsul A proconsul was an official of ancient Rome who acted on behalf of a consul. A proconsul was typically a former consul. The term is also used in recent history for officials with delegated authority. In the Roman Republic, military command, or ' ...

'', these facets are oriented in a

sagittal plane The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and div ...

. In

quadrupedal Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuo ...

monkeys these facets are oriented slightly differently due to their locomotor behaviour. In '' Oreopithecus'', a

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

hominid that became extinct , the orientation of the facet on the second metacarpal is similar to human conditions — an indication that it had the capability of pad-to-pad precision grip. ''Oreopithecus'' also lacks the waisted capitate associated with apes and climbing still present in ''

Australopithecus ''Australopithecus'' (, ; ) is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genus ''Homo'' (which includes modern humans) emerged within ''Australopithecus'', as sister to e.g. ''Austral ...

''.

Ossification

The metacarpal bone of the index finger has two centres of ossification: a primary centre in the shaft and a secondary centre in the head. This contrasts to the first metacarpal bone where the secondary centre is found in the base. The ossification process begins in the shaft during prenatal life, and in the head between 11th and 22nd months.

Additional images

File:Second metacarpal bone (left hand) - animation01.gif, Second metacarpal bone of the left hand (shown in red). Animation. File:Second metacarpal bone (left hand) - animation02.gif, Second metacarpal bone of the left hand. Close up. File:Gray219 - Second metacarpal bone.png, Palmer view of the left hand (second metacarpal shown in yellow). File:Gray220 - Second metacarpal bone.png, Dorsal view of the left hand (second metacarpal shown in yellow). File:Slide6val.JPG, Second metacarpal bone.Deep dissection.

Notes

References