Anal gland
The anal glands or anal sacs are small glands near the anus in many mammals. They are situated in between the external anal sphincter muscle and internal anal sphincter muscle. In non-human mammals, the secretions of the anal glands contain mostly volatile organic compounds with a strong odor, and they are thus functionally involved in communication. Depending upon the species, they may be involved in territory marking, individual identification, and sexual signalling, as well as defense (such as in skunks). Their function in humans is unclear.
Sebaceous glands within the lining secrete a liquid that is used for identification of members within a species. These sacs are found in many species of carnivorans, including wolves, bears, sea otters and kinkajous.