What is the name of the muscular organ where a fertilized egg develops into a baby?

The correct answer is the uterus. This hollow, muscular organ is essential for reproduction, as it provides the environment where a fertilized egg can implant and develop into a fetus during pregnancy. The structure of the uterus is specifically designed to support this process, with its thick, muscular walls that can expand to accommodate the growing baby and contract during childbirth. Additionally, the uterus has a lining known as the endometrium, which thickens in preparation for potential implantation of the fertilized egg and is shed during menstruation if implantation does not occur. This functional capacity is distinct from the other options; for example, the vagina serves as the birth canal and a passage for menstrual fluid, the ureter is involved in the transport of urine from the kidney to the bladder, and the ovary is responsible for producing eggs and hormones but does not facilitate the development of an embryo.