UTERUS, in comparative anatomy, a dilation in the walls of the oviduct for the preservation or development of the ova. In birds, although the ova are developed externally, the term uterus is often applied to that cavity where the eggs receive the shell. In most of the viviparous fishes, and in the viviparous lacertilia and ophidia the ova develop within the uterine cavity without any assistance or nourishment from the mother. In the Prototheria (=Orititho delpluia:=Illonotremata) the oviducts ac cording to some authorities, have no distinct uterine or Fallopian portiOn, but open directly into a cloacal chamber. Gegenbaur, however, calls the lower end of each oviduct a uterus. In the Meta theria (=Diclelphip = Mar supialia) each of the oviducts is differentiated into uterine and Fallopian tracts, opening into a long and distinct vagina. In the Eutheria ( =111onodelphio, including all other mammals) the uterus is variously modified. In the Primates it is normally single, though instances of a double uterus occasionally occur; it is two horned in the Ruminantia, Pachyder mata, Equidw, and Cetacea, and is said to be divided when it has only a very short body, which speedily divides exter nally and internally, and is continuous with the oviducts (as in most of the Car nivora and Edentate, and some of the Rodentia) ; it is actually double in some of the Edentata and in most of the Ro dentia, including the mouse and the hare, each oviduct passing into an intestim form uterus, which has two completely distinct openings lying near to each other within the vagina.
In human anatomy, a hollow, muscular organ, with very thick walls, situated in the pelvic cavity, between the rectum and the bladder. The virgin uterus is about three inches long, two broad, and one inch thick at its upper extremity. The middle part is called the body, the up per the fundus, and the lower, opening into the vagina, the neck. Its chief func tion is to receive the ovum from the Fal lopian tubes, and to retain and support it during the development of the foetus, which it expels by muscular contraction at parturition. During uterogestation the uterus becomes greatly enlarged and undergoes important structural changes; the uterus is liable to many affections and diseases, as tumors, ulceration, catarrh, tenesmus, hemorrhage, etc.