Light micrograph of a section of the human uterus about day 21 of the menstrual cycle. The inner lining of the uterus is known as endometrium and formed of simple tubular glands of epithelial cells. The depth of this layer varies during the menstrual cycle being narrow at the start but increasing in depth due to growth and elongation of the glands. If there is no pregnancy the glandular layer breaks down and contributes to the menstrual flow. The glands persist if pregnancy occurs and serve to support implantation of the conceptus. Most of the uterus is formed of a thick wall of smooth muscle (myometrium) beneath the glands. During labour the muscle contracts to expel the fetus at birth. Magnification x16 when narrow width printed at 10 cm.