<P> A primary ossification center is the first area of a bone to start ossifying . It usually appears during prenatal development in the central part of each developing bone . In long bones the primary centers occur in the diaphysis / shaft and in irregular bones the primary centers occur usually in the body of the bone . Most bones have only one primary center ( e.g. all long bones ) but some irregular bones such as the os coxa ( hip ) and vertebrae have multiple primary centers . </P>
when do primary ossification centers appear in an embryo
prenatal development