Castoreum

Castoreum ( /kæˈstɔriəm/) is the exudate from the castor sacs of the mature North American Beaver (Castor canadensis) and the European Beaver (Castor fiber). Within the zoological realm, castoreum is the yellowish secretion of the castor sac in combination with the beaver's urine, used during scent marking of territory. Both male and female beavers possess a pair of castor sacs and a pair of anal glands located in two cavities under the skin between the pelvis and the base of the tail. The castor sacs are not true glands (endocrine or exocrine) on a cellular level, hence references to these structures as preputial glands or castor glands are misnomers.