aberrant formation or incomplete differentiation of either of the small paired racemose (compound tubulo-alveolar) glands below the apex of the prostate in males, located posterolateral to the membranous portion of the urethra at the base of the penis, between the two layers of the fascia of the urogenital diaphragm, in the deep perineal pouch, and enclosed by transverse fibers of the sphincter urethrae membranaceae muscle; in mouse, bulbourethral glands are first identifiable at E17.5 and epithelial branching normally starts at postnatal day P1; during development, bulbourethral glands arise as epithelial outgrowths of the endodermal urogenital sinus invading the condensed mesenchyme flanking the primitive urethra; during subsequent development the epithelium branches extensively, filling the mesenchymal capsule and giving rise to the highly arborized ductal system of the mature organ