Brain: Rhombencephalon GraySubject = 187
Diagram depicting the main subdivisions of the embryonic vertebrate brain. These regions will later differentiate into forebrain, midbrain and hindbrain structures.
Superficial dissection of brain-stem. Lateral view.
NeuroNames	hier-531
MeSH	Rhombencephalon
Dorlands/Elsevier	r_12/12709581

The rhombencephalon (or hindbrain) is a developmental categorization of portions of the central nervous system in vertebrates.

The rhombencephalon can be subdivided in a variable number of transversal swellings called rhombomeres. In the human embryo we can distinguish eight rhombomeres, from caudal to rostral: Rh7-Rh1 and the isthmus (the most rostral rhombomere).

A rare disease of the rhomencephalon, "rhombencephalosynapsis" is characterized by a missing vermis resulting in a fused cerebellum. Patients generally present with cerebellar ataxia.

Myelencephalon

Rhombomeres Rh7-Rh4 form the myelencephalon.

The myelencephalon forms the medulla oblongata in the adult brain; it contains:

• a portion of the fourth ventricle,
• the glossopharyngeal nerve (CN IX),
• vagus nerve (CN X),
• accessory nerve (CN XI),
• hypoglossal nerve (CN XII),
• and a portion of the vestibulocochlear nerve (CN VIII).

Metencephalon

Rhombomeres Rh3-Rh1 form the metencephalon.

The metencephalon is composed of the pons and the cerebellum; it contains:

• a portion of the fourth ventricle,
• the trigeminal nerve (CN V),
• abducens nerve (CN VI),
• facial nerve (CN VII),
• and a portion of the vestibulocochlear nerve (CN VIII).

Additional images

Chick embryo of thirty-three hours’ incubation, viewed from the dorsal aspect. X 30.

Embryo between eighteen and twenty-one days.

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