[TA] relatively thin inner coat of smooth (involuntary) muscle bundles, mostly longitudinally arranged and separated from the epithelium by a thin vascular stroma of fibroelastic connective tissue, which are continuous superiorly with those of the prostatic urethra and peripherally with an outer, much more prominent layer of circularly oriented skeletal (voluntary) muscle fibers that form the main, tubelike part of the external urethral sphincter.external urethral sphincter of male. SYN: tunica muscularis partis intermediae urethrae masculinae [TA].