Question

which primary vesicle remains as the midbrain in the adult?
mesencephalon
prosencephalon
rhombencephalon
telencephalon

Explanation:

The embryonic primary brain vesicles include the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain). The mesencephalon does not further subdivide and develops directly into the adult midbrain. The prosencephalon splits into the telencephalon and diencephalon, while the rhombencephalon splits into the metencephalon and myelencephalon.

Answer:

Mesencephalon