Final answer:
The passageway from the third to fourth ventricle is called the cerebral aqueduct. It is located in the midbrain.
Step-by-step explanation:
The passageway from the third to fourth ventricle is known as the cerebral aqueduct. It connects the third ventricle, located between the left and right sides of the diencephalon, to the fourth ventricle, which is the space between the cerebellum and the pons and upper medulla. The cerebral aqueduct is located in the midbrain.