Which structure houses the developing fetus?

The developing fetus is housed in the uterus, which is a muscular organ located in the female reproductive system. The uterus expands as the fetus grows during pregnancy, providing a safe and controlled environment for development. It is lined with a specialized tissue that provides nutrients and support through the placenta, which is attached to the uterine wall.

The other structures mentioned do not serve the primary role of housing the fetus. The placenta is crucial for nutrient and gas exchange but is not a housing structure itself; it forms and attaches to the uterus. The vagina is the birth canal through which a baby is delivered but does not provide a space for fetal development. The cervix acts as the passageway between the uterus and vagina and plays a role during labor, but it does not contain the developing fetus. Thus, the uterus is the correct answer as it is specifically designed to support the growth and development of the fetus throughout pregnancy.