zone of bone organ ossification center FMA:75436 The first step in ossification of the cartilage is that the cartilage cells, at the point where ossification is commencing and which is termed a ossification center, enlarge and arrange themselves in rows. The matrix in which they are imbedded increases in quantity, so that the cells become further separated from each other. A deposit of calcareous material now takes place in this matrix, between the rows of cells, so that they become separated from each other by longitudinal columns of calcified matrix, presenting a granular and opaque appearance. Here and there the matrix between two cells of the same row also becomes calcified, and transverse bars of calcified substance stretch across from one calcareous column to another. Thus there are longitudinal groups of the cartilage cells enclosed in oblong cavities, the walls of which are formed of calcified matrix which cuts off all nutrition from the cells; the cells, in consequence, atrophy, leaving spaces called the primary areolC&. UBERON:0010355 center of ossification centrum ossificationis centrum ossificationis currently classified as a zone of a bone organ, but exists prior to bone ossifying ossification centre uberon