Illustration of a frontal (ventral) view of the human sacrum, part of the pelvic girdle. It is made up of five vertebrae that fuse during adulthood to form one stiff bone. As a lower part of the spine it is responsible for the ability to walk upright. It serves as a connection between body and legs and conducts main nerves through its foramina (holes). Beneath the sacrum is the coccyx (triangular), which is a rudimentary relic of a tail.