Marsupials have two uteri, each of which connect to a lateral vagina and which both use a third, middle "vagina" which functions as the birth canal. Marsupial embryos form a choriovitelline placenta (which can be thought of as something between a monotreme egg and a "true" placenta), in which the eggs yolk sac supplies a large part of the embryos nutrition but also attaches to the uterine wall and takes nutrients from the mothers bloodstream. However, bandicoots also have a rudimentary chorioallantoic placenta, similar to those of placental mammals. The fetus usually develops fully in placental mammals and only partially in marsupials including kangaroos and opossums. In marsupials the uterus forms as a duplex organ of two uteri. In monotremes (egg-laying mammals) such as the platypus, the uterus is duplex and rather than nurturing the embryo, secretes the shell around the egg. It is essentially identical with the shell gland of birds and reptiles, with which the uterus is homologous.In mammals, the four main forms of the uterus are: duplex, bipartite, bicornuate and simplex. Duplex
There are two wholly separate uteri, with one fallopian tube each. Found in marsupials (such as kangaroos, Tasmanian devils, opossums, etc. ), rodents (such as mice, rats, and guinea pigs), and lagomorpha (rabbits and hares). Bipartite
The two uteri are separate for most of their length, but share a single cervix. Found in ruminants (deer, moose, elk etc. ), hyraxes, cats, and horses. Bicornuate
The upper parts of the uterus remain separate, but the lower parts are fused into a single structure.
Support
The uterus is primarily supported by the pelvic diaphragm, perineal body, and urogenital diaphragm. Secondarily, it is supported by ligaments, including the peritoneal ligament and the broad ligament of uterus. Major ligaments
It is held in place by several peritoneal ligaments, of which the following are the most important (there are two of each):

Axis
Normally, the human uterus lies in anteversion and anteflexion. In most women, the long axis of the uterus is bent forward on the long axis of the vagina, against the urinary bladder. This position is referred to as anteversion of the uterus. Furthermore, the long axis of the body of the uterus is bent forward at the level of the internal os with the long axis of the cervix. This position is termed anteflexion of the uterus. The uterus assumes an anteverted position in 50% of women, a retroverted position in 25% of women, and a midposed position in the remaining 25% of women. Position
The uterus is located in the middle of the pelvic cavity, in the frontal plane (due to the broad ligament of the uterus). The fundus does not extend above the linea terminalis, while the vaginal part of the cervix does not extend below the interspinal line. The uterus is mobile and moves posteriorly under the pressure of a full bladder, or anteriorly under the pressure of a full rectum. If both are full, it moves upwards. Increased intra-abdominal pressure pushes it downwards. The mobility is conferred to it by a musculo-fibrous apparatus that consists of suspensory and sustentacular parts.