Translations:Kreuz- und Steißbein/18/en

The ventral side of the sacrum is characterized by a concave, smooth surface with a hollow (Facies pelvica). This side is oriented towards the pelvis. Four transverse struts are visible. Above these struts horizontal lines (Lineae transversae) are to be seen. These show the area where the individual vertebrae have grown together. At the same level as these lines, four paired openings in the bone can be seen, the Foramina sacralia anteriora.

The upper surface of the first sacral vertebra (S1) is directed upwards, towards the last lumbar vertebra. This surface is called the base ossis sacri. The widely protruding edge of this surface is called the promontorium. A wedge-shaped intervertebral disc lies between the fifth lumbar vertebra and this base. The caudal end of the sacrum tapers to a point and ends with the apex ossis sacri. There it joins the coccyx.