What is the name of the narrow gap between the vagina and the uterus that dilates during childbirth?

The narrow gap between the vagina and the uterus that dilates during childbirth is called the cervix. During the birthing process, the cervix plays a critical role as it opens to allow the baby to move from the uterus into the birth canal. This dilation is essential for a safe delivery, as it provides the necessary passage for the baby.

The cervix also functions as a barrier, protecting the uterus from infections and maintaining the pregnancy until the appropriate time for birth. In contrast, the options representing the vaginus, fallopian tube, and ovary refer to different structures in the female reproductive system, which do not serve the function of dilating at the time of childbirth. The vaginus is not a recognized term in human anatomy, the fallopian tubes are responsible for transporting eggs from the ovaries to the uterus, and the ovaries are responsible for producing eggs and hormones. Thus, the cervix is uniquely suited to the role described in the question.