Abstract

The bone development and the assessment of the fetal skeletal improvement turn into a basic segment in the behavior of a prenatal toxicity study. The sternum is a unique bone in the distinctive shape and development. This study focuses on the development of the sternum and the ribs attached in the whit New Zealand rabbit, Specimens were collected prenatally (n=30) and postnatally (n=30). A group of specimens were double stained for bone and cartilage using Alizarin Red and Alcian blue. Another group was scanned by CT. The sternum was consisted of manubrium, four sternebrae and xiphoid cartilage. The sternum was in communication with 6 pairs of ribs. 7 ossification centers appeared in the sternum, one for each segment except the fourth one which has two. The first group centers appeared in the manubrium and the first two sternebrae on 22 days old embryos. All primary centers seen before birth. There are no secondary ossification centers for the sternum. Concerning ribs, there are four ossification centers for each except the last two ribs. The ossification centers of the body came from the extension of the transvers process of the thoracic vertebrae and it appears as early as two weeks of gestation. By the end of the third week of pregnancy, the ribs show primary center of ossification from the second to the last one. The second center was designed for the head and it appeared two weeks after birth. The third and fourth centers for the tubercle appeared a month after birth. Complete fusion between these centers takes place in three months old rabbit.

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