Fine structure of tortoise skeletal muscle

Abstract

The fine structure of tortoise skeletal muscle was studied with the electron microscope. The packing of the A filaments (1.6 [mu] long) and the I filaments (2.35 [mu] long) within the myofibril is similar to that in frog twitch fibers. The position of the N line within the I band varied with the sarcomere length. The T [transverse] system tubules in these muscles formed a 3-dimensional network across the fibers at the level of the I band. On either side of the Z line it forms triad relationships with the other network of tubules of the sarcoplasmic reticulum.