Both beaver sexes have 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.[3] The castor sacs are not true glands (endocrine or exocrine) on a cellular level, hence references to these structures as preputial glands, castor glands, or scent glands are misnomers.[4]
^Svendsen, G.E., Huntsman, W.D, "A field Assay of Beaver Castoreum and Some of its Components". American Midland Naturalist, Vol. 120, No. 1 (Jul. 1988), pp. 144–149, University of Notre Dame. JSTOR2425894.