Scanning electron microscopic study of the fibrous rings of the arterial orifices in embryos of the 7(th) and 8(th) weeks.

The arterial fibrous rings were investigated in human embryos aged 7 and 8 weeks under light and scanning electron microscopes. In the present study it was shown that the arrangement of collagen and formation of fibres changes rapidly within one week. In the 7(th) week there are no collagen fibres and the netlike fibrils extend between processes of fibroblasts. At the end of the 8(th) week the collagen fibres are formed and they have different arrangements in the particular layers of the fibrous rings.