<P> There are two types of ossification centers--primary and secondary . </P> <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> <P> A secondary ossification center is the area of ossification that appears after the primary ossification center has already appeared--most of which appear during the postnatal and adolescent years . Most bones have more than one secondary ossification center . In long bones, the secondary centres appear in the epiphyses . </P>

The secondary ossification center in a long bone is located where