View source for Second metacarpal bone

{{Short description|Bone of the index finger}}
{{Use dmy dates|date=January 2024}}
{{Infobox Bone
|Name          = Second metacarpal bone
|Latin         = os metacarpale II
|Image         = Second metacarpal bone (left hand) 01 palmar view.png
|Caption       = Second metacarpal of the left hand (shown in red). Palmar view.
|Image2        = Gray230.png
|Caption2      = The second metacarpal. (Left.)
|Origins       =
|Insertions    =
|Articulations =
}}
The '''second metacarpal bone''' ('''metacarpal bone of the [[index finger]]''') is the longest, and its base the largest, of all the [[Metacarpus|metacarpal bones]].<ref name="Gray's">''[[Gray's Anatomy]]'' (1918). See infobox.</ref>

== Human anatomy ==
Its base is prolonged upward and medialward, forming a prominent ridge.<ref name="Gray's" />

It presents four articular facets, three on the upper surface and one on the [[ulna]]r side:<ref name="Gray's" />
* 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 muscle]] is inserted on the dorsal surface and the [[flexor carpi radialis muscle]] on the [[Anatomical terms of location#Hands and feet|volar]] surface of the base.<ref name="Gray's" /> The shaft gives origin to the first [[Palmar interossei muscles|palmar interosseus]] and the first and second [[Dorsal interossei of the hand|dorsal interossei]].

This bone is often the most prone to damage from fast bowlers in [[cricket]], 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.<ref>Laven, Kate. "West Indies' Courtney Walsh still in love with cricket." Daily Telegraph [London] 5 May 2009 Print.</ref>

== Evolution ==
The articulation between the second metacarpal and the capitate is considered uniquely specialized in [[hominid]]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 [[Opposability|opposition]] between the thumb and the index finger.  In contrast, in [[ape]]s, including fossil apes such as ''[[Dryopithecus]]'' and ''[[Proconsul (mammal)|Proconsul]]'', these facets are oriented in a [[sagittal plane]]. In [[Quadrupedalism|quadrupedal]] monkeys these facets are oriented slightly differently due to their locomotor behaviour.
<ref name="Moyà-Solà-1999">{{harvnb|Moyà-Solà|Köhler|Rook|1999 | loc= pp. 315–6}}</ref>

In ''[[Oreopithecus]]'', a [[Miocene]] hominid that became extinct {{mya|7}}, the orientation of the facet on the second metacarpal is similar to human conditions&nbsp;— 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]]''.
<ref name="Moyà-Solà-1999" />

== 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.<ref name=Ajay>{{cite journal|last=Balachandran|first=Ajay|author2=Anooj Krishna|author3= Moumitha Kartha|author4= Libu G. K.|author5= Liza John|author6= Krishnan B|title=A Study of Ossification of heads of 2nd to 5th Metacarpals in Forensic Age Estimation in the Kerala Population|journal=Journal of Evolution of Medical and Dental Sciences|date=30 December 2013|volume=2|issue=52|pages=10165–10171|doi=10.14260/jemds/1751|url=http://www.jemds.com/data_pdf/dr%20ajay%20balachandran.pdf|access-date=26 December 2013|doi-access=free}}</ref>

== Additional images ==
<gallery>
 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.
</gallery>

== See also ==
* [[Metacarpus]]
* [[First metacarpal bone]]
* [[Third metacarpal bone]]
* [[Fourth metacarpal bone]]
* [[Fifth metacarpal bone]]

== Notes ==
{{reflist}}

{{Gray's}}

== References ==
{{Commons category|Second metacarpal bone}}
* {{cite journal | doi = 10.1073/pnas.96.1.313 | last1 = Moyà-Solà | first1 = Salvador | pmc = 15136
 | last2 = Köhler | first2 = Meike | pmid = 9874815
 | last3 = Rook | first3 = Lorenzo
 | title = Evidence of hominid-like precision grip capability in the hand of the Miocene ape ''Oreopithecus''
 | journal = PNAS |date=5 January 1999 | volume = 96 | issue = 1 | pages = 313–317
 | url = http://www.pnas.org/content/96/1/313.full.pdf
| doi-access = free | bibcode = 1999PNAS...96..313M }}

{{Bones of upper extremity}}

{{Portal bar|Anatomy}}

[[Category:Skeletal system]]
[[Category:Bones of the hand]]
[[Category:Metacarpus]]