The uterus (ū ′ ter-̆u s; womb) is as big as a medium-sized pear (see figures 19.8 and 19.9). It is oriented in the pelvic cavity with the larger, rounded part directed superiorly. The part of the uterus superior to the entrance of the uterine tubes is called the fundus (f̆u n′ d̆u s). The main part of the uterus is called the body, and the narrower part, the cervix (ser′ viks; neck), is directed inferiorly. Internally, the uterine cavity in the fundus and uterine body continues through the cervix as the cervical canal, which opens into the vagina. The cervical canal is lined by mucous glands.
The uterine wall is composed of three layers: a serous layer, a muscular layer, and a layer of endometrium (see figure 19.9). The outer layer, called the perimetrium (per-i-mē ′ trē -̆u m), or serouslayer, of the uterus is formed from visceral peritoneum. The mid-dle layer, called the myometrium (mı̄ ′ ō -mē ′ trē -̆u m), or muscularlayer, consists of smooth muscle, is quite thick, and accounts forthe bulk of the uterine wall. The innermost layer of the uterus is the endometrium (en′ dō -mē ′ trē -̆u m), which consists of simple columnar epithelial cells with an underlying connective tissue layer. Simple tubular glands, called spiral glands, are formed by folds of the endometrium. The superficial part of the endometrium is sloughed off during menstruation.
The uterus is supported by the broad ligament and the roundligament. In addition to these ligaments, much support is providedinferiorly to the uterus by skeletal muscles of the pelvic floor. If ligaments that support the uterus or muscles of the pelvic floor are weakened, as may occur due to childbirth, the uterus can extend inferiorly into the vagina, a condition called a prolapsed uterus. Severe cases require surgical correction.