[Correlation between the processes of proliferation and differentiation in the histogenesis of somatic muscle tissue in birds].

The development of muscular tissue fibers has been studied in 8--19-day-old chick embryos by methods of electron microscopy, autoradiography and cytophotometry. Differentiated myogenic elements are derived from promyoblasts which devide during myogenesis at slightly changing parameters of the mytotic cycle. Promyoblasts fuse with each other or with symplasts or else can develop into myoblasts containing myofilaments in their cytoplasm. At later stages of myogenesis, some promyoblasts pass into "rest" condition with characteristic changes in the structure of nucleus, cytoplasm and muscular cells. These cells are situated between the basal and cytoplasmic membranes and identified as cell-satellites (myosatellites). They represent an important subpopulation of the muscular system, which preserve a certain ability to perceive stimuli to proliferation and differentiation, forming the cambial system of the skeletal-muscular tissue.