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The seat leg ( latin ischium or shortly ischium. Latinisierte form to ancient Greek ἰσχίον ischíon "hip, hip") is a paired flat bone and one of the components of the bony pelvis .


Human pelvis from the front. The ischium ( ischium ) is the lower part on both sides.

The ischium forms the lower arched border of the blocked hip hole ( foramen obturatum ). At the bottom it is thickened to form the ischial tuberosity ( tuber ischiadicum ). This serves as the origin of the muscle and as a seat point, with a pad of fat overlying it.

Above the ischial tuberosity is the ischial spine ( spina ischiadica ), which divides two sections in the pelvic line: Incisura ischiadica major , the large ischial bones, and Incisura ischiadica minor , the small ischial bones (both indentations can only be seen from the side and therefore not here pictured).

Remaining mammals

In most mammals, both ischial bones also participate in the formation of the pelvic symphysis , i.e. the fibrous cartilaginous connection between the two halves of the pelvis. This section is also known as the sciatic symphysis . Symphysis ischial and pubic symphysis ( pubic symphysis ) form here along the symphysis pelvina . The part lying to the side of the obturator foramen is called the ischial body ( corpus ossis ischii ). It forms the rear portion of the acetabulum ( acetabulum ). The part located medial to the obturator foramen is called the ischial branch ( Ramus ossis ischii ). Body and branch unite backwards (caudally) to form the ischial plate ( tabula ossis ischii ). Its posterior lateral cusp is the ischial tuberosity ( tuber ischiadicum ), from which various buttock muscles ( biceps femoris , semitendinosus , semimembranosus ) arise.

When viewed from behind, both ischial bones form a concave arch, the ischial arch ( ischial arc ). In male mammals, the penis is attached to the ischial bone section and this is where the penile muscles arise.

The spina ischiadica points upwards in the four-footed animals and has more the shape of a groin. In the quadrupeds, it still belongs to the iliac bone , but is still referred to as the ischiadic spine (pan crest ). The acetabular ridge also divides the major and minor ischiadic incisura , only the latter is still part of the ischium.


  • F.-V. Salomon: Bony skeleton. In: F.-V. Salomon et al. (Ed.): Anatomy for veterinary medicine. Enke-Verlag, Stuttgart 2004, ISBN 3-8304-1007-7 , pp. 37-110.

Web links

Wiktionary: ischium  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Federative Committee on Anatomical Terminology (FCAT): Terminologia Anatomica . Thieme, Stuttgart 1998, ISBN 3-13-115251-6 .