primary ossification centers appear in an embryo at birth.
when do primary ossification centers appear in an embryo?
at birth
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 except clavicle) but some irregular bones such as the os coxa (hip) and vertebrae have multiple primary centers.
ossification center
primary bone or the primary ossification center is the beginning of the bone building process during the first trimester. calcificed cartilage is basophilic and new bone being made is more acidophilic. 





























the primary ossification occurs in the diaphysis. in contrast, secondary ossification centers appear later at the epiphyses of the cartilage and develop similarly to the diaphysis.





























section::::clinical significance.:cancer.
primary bone