one of the three sections of the hipbone; situated below the ilium

The ventral and posterior of the three principal bones composing either half of the pelvis; seat bone; the huckle bone.

One of the pleurae of insects.

The ventral and posterior bone of each half of the pelvic girdle of Mammals; an ischiopodite.

Fracture of the ischium alone is rare. – Manual of Surgery Volume Second: Extremities--Head--Neck. Sixth Edition. by Alexander Miles Alexis Thomson

The furculum, or merry- thought, which is entire, marks the fore part of the trunk; the ischium, scapula, and most of the wing and leg bones are preserved, and there are impressions of the quill feathers and of down on the body. – The Antiquity of Man by Charles Lyell

It arises above from the inferior surface of the ischium, and from the tuberosity of the same bone. – Artistic Anatomy of Animals by Édouard Cuyer

It originates at the arch of the ischium and extends forward between the thighs. – Common Diseases of Farm Animals by R. A. Craig, D. V. M.