The ultrastructure of the organic matrix of calcified cartilage and bone in embryonic mouse radii

Abstract

It was found that in embryonic mouse radii the organic matrix of both calcified cartilage and bone is surrounded by a border of moderate electron density. The chemical composition of this structure is still unknown although we found proof that the border does not contain an appreciable amount of Thorotrast-stainable mucopolysaccharides. Where bone formation has just begun small islands of calcification can be found. The organic matrix of these islands contains Thorotrast-stainable mucopolysaccharides. Collagen fibrils, however, are absent. Only later on, when the islands become confluent, the fibrils between them become part of the bone matrix. In a certain phase of development the diaphyseal shaft of a radius consists of an inner layer of calcified cartilage and an outer, thicker one of bone tissue.