Final answer:
The midbrain originates from the mesencephalon, one of the embryonic primary vesicles, and is associated with the cerebral aqueduct, the ventricle that connects the third and fourth ventricles.
Step-by-step explanation:
The midbrain is derived from the embryonic primary vesicle known as the mesencephalon, which does not differentiate into any finer divisions and remains as the established region of the midbrain. In contrast, the primary vesicle of the rhombencephalon further develops into the hindbrain, which includes the pons, cerebellum, and medulla. The ventricle associated with the midbrain is known as the cerebral aqueduct, which passes through the center of the midbrain connecting the third and fourth ventricles.