A distinctive organ found in elasmobranchs, the rectal gland was first described in 1645. Its structure would later become well defined but not its function. The gland size and shape varies among species and, in some, takes the form of a disaggregated tissue in the submucosa of the rectum. Histological studies revealed a remarkably well-conserved structure across species of blunt end tubules arranged radially around a central canal lined by cuboidal cells intricately intertwined with one another with extensive basolateral infoldings. The gland is supplied with blood via the posterior mesenteric artery that branches into anterior and posterior rami that give rise to circumferential branches. The arteries give rise to sinusoids that course among the secretory tubules and collect in sinuses that give rise to a central vein that continues into the intestinal vein. The gland is amply supplied with nerves that form a dense plexus of fibers within the capsule and branch out into the parenchyma of the gland coursing around the tubules. Embryologically the glands develop from a bud that arises from the gut endoderm. The proposed functions for the rectal gland included digestive, reproductive, and excretory roles, none of which proved to be reasonable or adequate.