The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, or as a pair the sitting bones, is a large swelling posterior (anatomy), posteriorly on the superior ramus of the ischium, superior ramus of the ischium. It marks the lateral boundary of the pelvic outlet.
When sitting, the weight is frequently placed upon the ischial tuberosity. The Gluteus maximus muscle, gluteus maximus provides cover in the upright posture, but leaves it free in the seated position.
[Platzer (2004), p 236] The distance between a cyclist's ischial tuberosities is one of the factors in the choice of a bicycle saddle.
Divisions
The tuberosity is divided into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, quadrilateral portion.
* The ''lower portion'' is subdivided by a prominent longitudinal ridge, passing from base to apex, into two parts:
** The outer gives attachment to the adductor magnus
** The inner to the sacrotuberous ligament
* The ''upper portion'' is subdivided into two areas by an oblique ridge, which runs downward and outward:
** From the upper and outer area the semimembranosus arises
** From the lower and inner, the long head of the biceps femoris and the semitendinosus
Additional images
File:Tuberosity of the ischium.PNG, Muscles of the gluteal and posterior femoral regions, with ischial tuberosity highlighted in red
File:Gray235.png, Right hip bone. External surface.
File:Gray236.png, Right hip bone. Internal surface.
File:Gray237.png, Plan of ossification of the hip bone
File:Gray239.png, Diameters of inferior aperture of lesser pelvis (female)
File:Gray339.png, Right hip-joint from the front
File:Gray436.png, The obturator externus
File:Slide3ADA.JPG, Anterior view of the pelvis with the ischial tuberosity labelled in the lower part of the image
See also
* Ischial bursitis
* Sitting disability
Notes
References
*
*
External links
* - "The Female Perineum: Bones"
* - "Major Joints of the Lower Extremity: Hip bone (lateral view)"
* (, , )
{{Authority control
Bones of the pelvis
Ischium