Menstruation (mammal)
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated sexually reproductive-age females of certain mammal species.
Cervix
Female marsupials have paired uteri and cervices. Most eutherian (placental) mammal species have a single cervix and single, bipartite or bicornuate uterus. Lagomorphs, rodents, aardvarks and hyraxes have a duplex uterus and two cervices. Lagomorphs and rodents share many morphological characteristics and are grouped together in the clade Glires. Anteaters of the family myrmecophagidae are unusual in that they lack a defined cervix; they are thought to have lost the characteristic rather than other mammals developing a cervix on more than one lineage. In domestic pigs, the cervix contains a series of five interdigitating pads that hold the boar's corkscrew-shaped penis during copulation.