Sacrum caudal and thoracic vertebrae to form a single structure called the synsacrum. In the frog the ilium is elongated and forms a mobile joint with the sacrum that acts as an additional limb to give more power to its leaps. Sacrum The sacrum ( or ; plural: "sacra" or "sacrums"), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of sacral vertebrae S1S5 between 18 and 30years of age. The sacrum is situated at the upper, back part of the pelvic cavity, between the two wings of the pelvis. It
Sacrum unclear. Supposedly the sacrum was the part of an animal offered in sacrifice (since the sacrum is the seat of the organs of procreation). Others attribute the adjective ἱερόν to the ancient belief that this specific bone would be indestructible. As the Greek adjective ἱερός may also mean "strong", it has also been suggested that "os sacrum" is a mistranslation of a term intended to mean "the strong bone". This is supported by the alternative Greek name μέγας σπόνδυλος by the Greeks, translating to "large vertebra", translated into Latin as "vertebra magna". In Classical Greek the bone was known as