the inner one-third of the myometrium (termed the "junctional" or "sub-endometrial" layer) appears to be derived from the müllerian duct, while the outer, more predominant layer of the myometrium appears to originate from non-müllerian tissue, and is the major contractile tissue during parturition and abortion. the junctional layer appears to function like a circular muscle layer, capable of peristaltic and anti-peristaltic activity, equivalent to the muscular layer of the intestines.