Sacrum lumbar vertebra, and its lower part with the coccyx (tailbone) via the sacral and coccygeal cornua. The sacrum has three different surfaces which are shaped to accommodate surrounding pelvic structures. Overall it is concave (curved upon itself). The base of the sacrum, the broadest and uppermost part, is tilted forward as the sacral promontory internally. The central part is curved outward toward the posterior, allowing greater room for the pelvic cavity. In all other quadrupedal vertebrates, the pelvic vertebrae undergo a similar developmental process to form a sacrum in the adult, even while the bony tail (caudal) vertebrae remain unfused.
Ver sacrum of Indo-Iranian human and warrior gods with animal forms: among the Iranian god of victory "V(e)r(e)thragna" 's incarnations, seven are of animal form, including the bull, horse, boar and hawk, each of which is associated at one time or another with a "ver sacrum" and Roman army insignia. On the "recto" of coins from Campania appears a human character bearing over his head that of a boar, and on the "verso" the word "ROMA". German scholar C. Koch interprets this character as god Quirinus, since he identifies the boar, "aper", as the animal symbol of the god. Dumézil remarks that