Ischium is a thick, rough-surfaced prominence below the lesser sciatic notch. This is the portion that supports weight while sitting (especially noticeable on a hard surface) and can be felt simply by sitting on the fingers. It serves as the origin for the inferior gemellus muscle and the hamstrings. 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 ischial ramus joins the inferior ramus of the pubis anteriorly and is the strongest of the hip
Aphanosauria "Marasuchus" (other avemetatarsalians) have their ischia only slightly contact at the middle portion of each bone. The tip of the ischium is also rounded and semi-triangular in cross-section, with the lateral (outer) face of each ischium thinning towards the lower edge of the bone while the medial (inner) face is flat and contacts the other ischium. Poposauroids and dinosaurs also have rounded ischia, but lack the semi-triangular shape, which is also known in "Asilisaurus". The ischium also has a groove on the upper part of the shaft. Unlike dinosaurs, aphanosaurs have an acetabulum (hip socket) which is closed up by