Metacarpal bones

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Metacarpal bones of the human left hand

The metacarpal bones ( ossa metacarpi , MC) form the bony basis of the metacarpal between the wrist and fingers . These are tubular bones that are subdivided into a base ( base metacarpi ), a body ( corpus metacarpi ) and the head ( caput metacarpi ), which is in the direction of the finger bone .

The elasticity of the hand is guaranteed by the structure of the metacarpal . In addition, the first metacarpal bone is significantly involved in the comparison ( opposition ) of the thumb to other fingers.

Metacarpal bones of man

Human hand, metacarpal brown

In humans there are a total of five metacarpal bones, which are arranged almost parallel. The second and third metacarpal bones are the longest, the first is the shortest. The spaces between the metacarpal bones ( Spatia interossea metacarpi ) are filled by the interossei muscles . The five metacarpal bones are numbered further from the trunk ( lateral ) to the trunk ( medial ), with the slightly splayed first metacarpal bearing the thumb :

  • Os metacarpale primum (MC I) or Os metacarpale pollicis ("metacarpal bone of the thumb")
  • Second metacarpal bone (MC II)
  • Os metacarpale tertium (MC III)
  • Os metacarpale quartum (MC IV)
  • Os metacarpale quintum (MC V)

The broad base of the metacarpal bones has a basic cubic shape. Their inwardly curved ( concave ) hyaline cartilage surfaces are connected to the distal row of the carpal bones ( ossa carpi ) of the wrist ( carpus ) and together form the carpometacarpal joints , the first of which is called the thumb saddle joint . The base of the third metacarpal bone has a stylus extension ( processus styloideus ) to which the extensor carpi radialis brevis muscle attaches.

The shaft has a triangular cross-section. In the basic anatomical position - also known as the anatomical zero position (palms facing forward) - the tip of the triangle points forward, the base towards the back of the hand. In the distal section of the metacarpal bones, this side is an almost flat bone surface over which the tendons of the extensors run. The other two sides, that is, the medial and lateral sides of the metacarpal bones, are curved inwards. This is where the interossei muscles begin . At the front they collide in a bone ridge.

The head of the metacarpal bones has an outwardly curved ( convex ) cartilage surface, the extent of which is greater in the anterior-posterior ( anterio-posterior ) direction than in the horizontal ( transversal ) direction. These cartilage surfaces form the joint head of the metatarsophalangeal joints . On both sides of the head there are small bumps ( tubercula ). The five finger rays of the hand start from here. The metacarpal is taut and stabilized by ligaments ; the lateral ligaments (collateral ligaments) of the metacarpophalangeal joints are attached to the cusp. The head of the first metacarpal bones has two small joint facets on the palm side, which serve to connect with the sesamoid bones of the abductor pollicis brevis and flexor pollicis brevis muscles .

Comparative anatomy

Comparative anatomical representation of the hand skeleton

In running animals, the reduction in the number of front toes also leads to regression and / or fusion of the bones in the metacarpal area. Thus, in horses a strong metacarpal (MC III, "only Röhrbein ") formed of the ( "MC II and IV on both sides by a thin metacarpal splint bones ") is flanked.

Birds only have one metacarpal bone, which is fused with the lower row of the carpal bones and is called the carpometacarpus (→ bird skeleton ).

literature

  • Walther Graumann, Rolf Baur: the musculoskeletal system. In: Compact Textbook Anatomy. Vol. 2, Schattauer, Stuttgart 2004, ISBN 3-7945-2062-9 , pp. 316-317.
  • Franz-Viktor Salomon: Bony skeleton. In: Franz-Viktor Salomon et al. (Hrsg.): Anatomie für die Tiermedizin. Enke-Verlag Stuttgart, 2nd ext. Edition 2008, ISBN 978-3-8304-1075-1 , pp. 37-110.

Web links

Commons : Human metacarpus  - collection of images, videos and audio files
Wiktionary: metacarpal bones  - explanations of meanings, word origins, synonyms, translations