Ossification center - wikipedia Ossification center This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( May 2011 ) Ossification center X-ray of ossification centers in a child. Details Identifiers Latin centrum ossificationis Dorlands / Elsevier 12227335 TA A02. 0.00. 043 FMA 75436 Anatomical terminology ( edit on Wikidata ) The first step in ossification of the cartilage is that the cartilage cells, at the point where ossification is commencing and which is termed as an 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 areolæ. Types of ossification centers Section of fetal bone of cat. ir. Irruption of the subperiosteal tissue. p. Fibrous layer of the periosteum. o. Layer of osteoblasts. im. Subperiosteal bony deposit. There are two types of ossification centers -- primary and secondary. 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. 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. References This article incorporates text in the public domain from the 20th edition of Gray 's Anatomy ( 1918 ) Jump up ^ Gray and Spitzka ( 1910 ), page 44. Bibliography Gray, Henry ; Spitzka, Edward Anthony ( 1910 ). Anatomy, descriptive and applied. the University of California : Lea & Febiger. Development of bone Ossification Triradiate cartilage Limb development Limb bud Apical ectodermal ridge Zone of polarizing activity Sclerotome Myotome Septum transversum Retrieved from `` https://en.wikipedia.org/w/index.php?title=Ossification_center&oldid=808049222 '' Categories : Wikipedia articles incorporating text from the 20th edition of Gray 's Anatomy ( 1918 ) Skeletal system Tissues ( biology ) Hidden categories : Articles needing additional references from May 2011 All articles needing additional references Medicine infobox template using GraySubject or GrayPage Medicine infobox template using Dorlands parameter Talk About Wikipedia Nederlands Edit links This page was last edited on 31 October 2017, at 15 : 42. About Wikipedia

Question: when do primary ossification centers appear in an embryo
Answer: prenatal development