UNIQUE ULTRASTRUCTURAL CHARACTERISTICS OF PIGEON ANTERIOR LATISSIMUS-DORSI MUSCLE

The pale anterior latissimus dorsi (ALD) muscle of the adult pigeon wa s studied ultrastructurally. There were embryonic heart and skeletal m uscle features present. These included loosely packed myofibrillar app aratus, subsarcolemmal pads of sarcoplasm, abundant pinocytotic vesicl es, and tubular aggregates. The latter were focal, smooth surfaced, an d bilaminar. An increased accumulation of Z-disk material was widespre ad in the muscle fibers. There were distinct sarcolemmal evaginations which possess knob-like projections. Myocellular extensions were evide nt at muscle fiber ends and these produced bud-like configurations in transverse section. These features in the normal adult ALD rules out t he assumption that they represent a denervation phenomenon, as suggest ed by others.