The striped muscular tissue, which gives the muscle its power of contracting, is found when examined by the microscope to be made up of extremely slender muscular fibres, each about one inch in length, but most of them less than 1/500 of an inch across.

Each muscular fibre has externally a thin sheath or envelope, the sarcolemma, which envelopS the contracting part of the fibre. This latter is soft and almost semi-fluid, and under a microscope is seen to present a striped appearance, as if made up of alternating dimmer and brighter transverse bands (Fig. 33). After death the semi-solid contents of the fibre solidify and death-stiffening is produced ; at the same time the fibre often splits up into a number of very fine threads or fibrillú, which were formerly regarded as true constituents of the living muscular fibre.