This thesis is centred on a unique feature of the skeletal muscle fibre, the satellite cell. This small fusiform cell, lying in a subsarcolemmal position, is the most recently discovered cytological entity of skeletal muscle. It can be readily distinguished from other better-known mononuclear cells found lying between muscle fibres, such as endomycial fibroblasts, vascular pericytes, mast cells and histiocytes. It is unique in that it is the only mononucleated cell lying within the basement membrane of the normal adult muscle fibreo Mononuclear cells are, however, a prominent feature of developing and regenerating muscle. In both, myoblasts fuse to form myotubes, which in turn develop into mature fibres. The immediate inference from this is that the satellite cell could be related to the mononuclear cells seen in these two situations.