Ischium the Latin term derives from Greek ἰσχίον "iskhion" meaning "hip joint". The division of the "acetabulum" into "ischium" (ἰσχίον) and "ilium" (λαγών, "os lagonicum") is due to Galen, "De ossibus". Galen, however, omits mention of the "pubis" as a separate bone. The clade Dinosauria is divided into the Saurischia and Ornithischia based on hip structure, including importantly that of the ischium. In the majority of dinosaurs, the ischium extends down from the ilium and towards the tail of the animal. The acetabulum, which can be thought of as a "hip-socket", is a cup-shaped opening on each side of the pelvic
Squamous part of occipital bone The lower division of the cruciform eminence is prominent and is named the internal occipital crest; it bifurcates near the foramen magnum and gives attachment to the falx cerebelli. In the attached margin of this falx is the occipital sinus, which is sometimes duplicated. In the upper part of the internal occipital crest, a small depression is sometimes distinguishable; it is termed the vermian fossa since it is occupied by part of the vermis of the cerebellum. Transverse grooves, one on either side, extend from the internal occipital protuberance to the lateral angles of the bone; those grooves accommodate the