derived from the cloacal folds; in male embryos, they close over the urethral plate and fuse to form the spongy urethra and ventral aspect of the penis; in female embryos, the unfused urogenital folds develop into the labia minora."http://medical-dictionary.thefreedictionary.com/urogenital+folds
"After the onset of sexual differentiation at the end of the seventh week of foetal development, the urogenital sinus opens on the surface of the perineum. The genital tubercle is a midline swelling that grows at the cephalic end. Posterior to this, a urethral fold forms on either side of the urogenital membrane. Labial swellings then form lateral to each of the urethral folds. The testes ultimately descend into the labial swellings, which become distended and move medially to form the scrotum by fusion of each labial fold, forming the median scrotal raphe."
"Staged rotation flap scrotoplasty and orchidopexy in a patient with inguinal ectopic scrotum." Journal of Surgical Case Reports. 2015 Oct; 2015(10): rjv137. PMCID 4626801. doI:10.1093/jscr/rjv137.
"Fusion of the urethral folds in humans results in formation of the urethra proper internally and penile raphe externally, a structure that is not seen in the mouse."
"An illustrated anatomical ontology of the developing mouse lower urogenital tract." Development. 2015 May 15; 142(10): 1893-1908. PMCID 4440924. doi:10.1242/dev.117903.
"Bulbospongiosus muscles are fused in a midline raphe in males and separated in females."http://www.unmc.edu/dissection/idg29perineum.cfm
"Anococcygeal Raphe Revisited: A Histological Study Using Mid-Term Human Fetuses and Elderly Cadavers." Yonsei Medical Journal. 2012 Jul 1; 53(4): 849-855. PMCID 3381476. doi:10.3349/ymj.2012.53.4.849.