1. (Anat.) (a) An organ which, by its contraction, produces motion. See Illust. of Muscles of the Human Body, in Appendix. (b) The contractile tissue of which muscles are largely made up. Note: Muscles are of two kinds, striated and nonstriated. The striated muscles, which, in most of the higher animals, constitute the principal part of the flesh, exclusive of the fat, are mos...