Developing Elastic Fibers in the Chick Embryo

Abstract

The tunica media of the developing chick aorta was examined for elastic fiber formation. Embryos of three to eighteen days incubation age were prepared for electron microscopy by Karnovsky's fixation. Small embryos were fixed by “in toto” immersion: medium sized embryos were previously transected. The aortae of larger embryos were removed prior to fixation. Epon 812 was used for embedment.Irregular masses of amorphous ground substance appeared in the interstitial space of the aortae in three to five day embryos. These masses were located where elastic fibers would later form (Fig. 1). Later loose tangles of microfibrils appeared within the same masses (Fig. 2). In still older embryos, individual unit collagen fibrils appeared within this loose network. At one week's incubation, small elastic fibers could be identified by their homogeneous matrix. These arose within the conglomerate masses described above. At the beginning of the third week compact bundles of colinear unit collagen fibrils appeared (Fig. 3). These fibrils swelled, gradually lost their periodicity and became very lucid (Fig. 4).