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(Science: anatomy) A ringlike band of muscle fibres that constricts a passage or closes a natural orifice, also called musculus sphincter.

Origin: L., Gr. Sphinkter = that which binds tight A ring of muscle that contracts to close an opening.A normally contracted muscle that serves the purpose of blocking or opening a tube to allow materials to pass through. The best known example of a sphincter is the anal sphincter which opens to expel faeces to the external environment from the body when r.