an examining thumb is placed over the posterosuperior spine of the sacrum and then made to slide, first outward and then inward. If on pressure over the former point tenderness is detected, it is due to a sensitive deposit in the structures of the gluteal aspect of the posterosuperior spine. If the tenderness is over the inner point, it is probable that the superior ligaments of the sacroiliac joint are strained and sensitive. If the tenderness is increased by pressure backward on the anterosuperior aspect of the ilium and decreased by pulling forward the crest from behind, this is positive proof that it is caused by the sensitive ligaments.