A rhesus macaque uterus from an early menstruating animal 48 hours after P withdrawal. For this photograph the uterus has been separated from the cervix and cut in half along the longitudinal axis. A black line has been drawn to delineate the endometrial-myometrial border. The beginning of tissue bleeding is evident in the functionalis zone. The black dashed line shows the full-thickness plane for histological sectioning. Endo = endometrium; Myo = myometrium.