The ligaments of the sacro-iliac joint were dissected in 51 adult and 11 full-term fetal specimens, and a no. of features not previously descr. were recorded. The elevations to which these ligaments are attached were examined in a no. of dried, adult specimens (75 hip-bones and 64 sacra). It was found that (1) The sacrum and ilium are held in apposition by a capsular ligament and a no. of accessory ligaments dorsal to it. (2) The striking feature of all the accessory ligaments in adults is that they are arranged in 2 distinct cranial and caudal groups of fasiculi, the former passing dorsally and laterally, and the latter cranially, from their sacral attachments; this disposition is not found in fetal specimens. The significance of these arrangements is discussed and related to movements of the sacrum observed in the living.