MUSCLE

(Lat. musculus, diminutive of mus, a mouse, from its resemblance to a flayed mouse.) Fleshy fibres susceptible of contractions and relaxations. Some of the muscles are obedient to the will, and therefore called voluntary; others, such as the heart, are independent of the will, or involuntary; and others, as the diaphragm and muscles of respiration generally, have a mixed action, being to a certain extent only dependent upon the will. Muscles are aggregates of minute muscular fibres, which appear to be composed of small globules; but we are, in fact, ignorant of the ultimate structure of the muscles, and of the causes on which their wonderful powers depend. They are enveloped in and penetrated by cellular membrane, and abundantly supplied by nerves, blood ve els, and lymphatics. Their principal constituent or proximate elementary structure consists of albumen, besides which gelatin and fat are derived from their cellular membrane; and haem a to sin, osmazome, and other constituents of the blood are [s. 794]