Abstract
1. The fine structure of tortoise skeletal muscle has been studied with the electron microscope.
2. The packing of the A filaments (1·6 μ long) and the I filaments (2·35 μ long) within the myofibril is similar to that in frog twitch fibres.
3. The position of the N line within the I band is found to vary with the sarcomere length.
4. The T-system tubules in these muscles form a three-dimensional network across the fibre 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 sarco-plasmic reticulum.
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Selected References
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