Which structures comprise the myelencephalon (hindbrain)?

• A. Medulla and some reticular formation
• B. Pons and cerebellum
• C. Midbrain and thalamus
• D. Cerebral hemispheres

Answer: (A)

The myelencephalon is the caudal part of the brainstem that becomes the medulla oblongata, which houses vital autonomic centers and cranial nerve nuclei. The reticular formation is a diffuse network that runs through the brainstem and extends into the medulla, so the structures that comprise the myelencephalon are the medulla plus parts of the reticular formation. The pons and cerebellum come from the neighboring metencephalon, while the midbrain and thalamus are from higher embryonic regions (mesencephalon and diencephalon), and the cerebral hemispheres are forebrain. Therefore, medulla and some reticular formation best fit the myelencephalon.