Contribution to the study of the development and ossification of human sternum.

We have studied the development of sternum in man. Complete microscopic series of sections through thorax of human embryos and fetuses from the second and third months of gestation served as the research material. Preparations were stained by Alcian blue and Mayer's haematoxyline, counterstained by eosine. We also had a set of macroscopic preparations of sterna and adjacent parts of ribs from fetuses of the fifth and sixth months of gestation. These specimens were stained by Alcian blue and by Alizarine and subsequently cleared by glycerine method. We have found that sternum develops by a fusion of sternal bars. Sternal bars develop from anterior bent parts of ribs, lying one over another like tiles. The newly formed sternum has different proportions in comparison to its definitive state. In all the cases its manubrium is wider and bigger, its xiphoid process is longer, in almost all the cases doubled or at least bifurcated. The sternocostal junctions are provided with interzones with the exception of the first rib. Its primordium continues into sternum without any border. Clavicle is connected with sternal anlage without any visible border and this interzone quickly develops as the primordia of the sternoclavicular articulation and the disc. In the medial part, there is a cartilaginous model which ossifies very early--as the first bone of the body. In young embryos from the end of the second month of gestation the clavicle and sternum show very different structures. Ossification of the sternum begins in the fifth month by developing a large number of very small centers of ossification which are not yet detectable by X-ray or CT.(ABSTRACT TRUNCATED AT 250 WORDS)