[TA] innermost layer of urethra including an epithelium typical of the urinary tract (a transitional epithelium or urothelium) proximal to the openings of the ejaculatory ducts and typical of the genital tract (a stratified columnar epithelium) distally that continues through the intermediate and most of the spongy urethra, changing again to a stratified squamous epithelium in the region of the navicular fossa; many recesses occur in the mucosa of the spongy portion that continue into tubular, branching mucous glands.mucosa of the intermediate part of the male urethra, mucosa of the prostatic part of the male urethra, mucosa of spongy part of the male urethra SYN: mucous membrane of male urethra.