The<unk>  is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones.  Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx (tailbone).
It is curved upon itself and placed obliquely (that is, tilted forward).  It is concave facing forwards, thus its curvature is considered a kyphosis.  The base projects forward as the sacral promontory internally, and articulates with the last lumbar vertebra to form the prominent sacrovertebral angle.  The central part is curved outward towards the posterior, allowing greater room for the pelvic cavity.
Sacrum
Torso
Scalp
Humerus
Dorsum 
Axilla
Trapezium 
Calcaneus