The uterus is a muscular organ with thick walls, two upper openings to the fallopian tubes and an inferior opening to the vagina. Update Date: 09/03/2008D. Scott Smith, M.D., MSc, DTM&H, Chief of Infectious Disease & Geographic Medicine, Kaiser Redwood City, CA & Adjunct Assistant Professor, Stanford University. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.