Feilization of a secondary oocyte by a spermatozoan usually occurs in the

After the secondary oocyte is released from the ovary, it is captured by the fimbriae of the uterine tube. In the uterine tube, the oocyte enters the funnel-shaped infundibulum, reaches the abdominal ostium, and passes through the ampulla. Here, a spermatozoan typically feilizes the oocyte. The feilized ovum or the unfeilized secondary oocyte then moves through the narrow isthmus of the uterine tube to reach the intramural or uterine poion of the tube (that pan of the tube that is within the wall of the uterus). After the feilized ovum enters the uterus, it implants in the uterine wall. By this time, the embryo has developed into the blastocyst stage. If passage of the feilized ovum through the uterine tube is restricted, implantation into the tubal wall may occur.