The Uterus is a hollow, thick-walled, muscular organ. Its function is to recieve, retain, and nourishfertilized ovum. The regions are the body (major portion), fundus (rounded superior region), isthmus (which is a narrowed inferior region), the cervix (narrow neck, or outlet, and projects into the vagina), and finally the cervical canal that communicates with the vagina via external os and the uterine body via internal os.