n :  an outer layer of smooth muscle surrounding a hollow or tubular organ (as the bladder, esophagus, large intestine, small intestine, stomach, ureter, uterus, and vagina) that often consists of an inner layer of circular fibers serving to narrow the lumen of the organ and an outer layer of longitudinal fibers serving to shorten its length - called also muscularis externa , tunica muscularis  .
 
 
 
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