The sacrum consists of five sacrums, which are divided into the base, side, tip, pelvic surface and dorsal surface of the sacrum. It is an inverted triangle, forming the posterior upper wall of pelvic cavity. Its lower end is the sacral apex, which is related to the coccyx. The broad base at the upper end forms a lumbosacral angle with the fifth lumbar vertebra. The pelvic surface of sacrum is concave and the dorsal surface is convex to increase pelvic capacity. There are obvious gender differences in sacrum, male is long and narrow, female is short and wide, which meets the needs of female delivery.

The sacrum consists of five sacrums, which are divided into the base, side, tip, pelvic surface and dorsal surface of the sacrum. It is an inverted triangle, forming the posterior upper wall of pelvic cavity. Its lower end is the sacral apex, which is related to the coccyx. The broad base at the upper end forms a lumbosacral angle with the fifth lumbar vertebra. The pelvic surface of sacrum is concave and the dorsal surface is convex to increase pelvic capacity. There are obvious gender differences in sacrum, male is long and narrow, female is short and wide, which meets the needs of female delivery.

Reference: Sacrum-Baidu Encyclopedia