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The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, [1] or as a pair the sitting bones, [2] is a large posterior bony protuberance on the superior ramus of the ischium. It marks the lateral boundary of the pelvic outlet.
The superior ramus is a partial origin for the internal obturator and the external obturator muscles. The inferior ramus serves partially as origin for part of the adductor magnus muscle and the gracilis muscle. The inferior ischial ramus joins the inferior ramus of the pubis anteriorly and is the strongest of the hip (coxal) bones.
Its oblique fibres descend laterally, converging to form a thick, narrow band that widens again below and is attached to the medial margin of the ischial tuberosity. It then spreads along the ischial ramus as the falciform process, whose concave edge blends with the fascial sheath of the internal pudendal vessels and pudendal nerve.
It is divisible into three portions: the body, the superior ramus, and the inferior ramus. The body forms approximately one-third of the acetabulum. The ischium forms a large swelling, the tuberosity of the ischium, also referred to colloquially as the "sit bone". When sitting, the weight is frequently placed upon the ischial tuberosity.
The ischiopubic ramus is a compound structure consisting of the following two structures: from the pubis, the bones inferior pubic ramus; from the ischium, the inferior ramus of the ischium; It forms the inferior border of the obturator foramen and serves as part of the origin for the obturator internus and externus muscles.
These terms are derived from tuber (Latin: swelling)., [8] as is also protuberance, which occasionally is synonymous with "tuberosity". A ramus (Latin: branch) refers to an extension of bone, [9] such as the ramus of the mandible in the jaw or superior pubic ramus. Ramus may also be used to refer to nerves, such as the ramus communicans.
The subpubic angle (or pubic angle) is the angle in the human body as the apex of the pubic arch, formed by the convergence of the inferior rami of the ischium and pubis on either side. The subpubic angle is important in forensic anthropology , in determining the sex of someone from skeletal remains.
The lesser sciatic foramen is an opening between the pelvis and the back of the thigh. The foramen is formed by the sacrotuberous ligament which runs between the sacrum and the ischial tuberosity and the sacrospinous ligament which runs between the sacrum and the ischial spine.