Two forms of pre-auricular groove may be distinguished on the iliac bone. One form occurs in both male and female, and marks the attachment of the inferior part of the ventral sacro-iliac ligament. The second form is found only in some female pelves. It resembles the markings of pregnancy and childbirth on the posterior aspect of the public symphysis, and like them is a result of the physiological and pathological changes occurring at the site of attachment of the pelvic joint ligaments during this time. However, because of the greater strain borne by the sacro-iliac joints, the pre-auricular groove, in conjunction with the marking of the interosseous ligament of the joint, is a more sensitive indicator of past pregnancy and childbirth than is the pubic bone.