Human Anatomy - Kotsan I. Y. 2009

Brain
Isthmus of the hindbrain

The ISTHMUS OF THE rhombencephalon (isthmus rhombencephali) is the narrowest part of the Brainstem, located between the Midbrain and the Hindbrain. The isthmus of the rhombencephalon includes the superior cerebellar peduncles (pedunculi cerebellares superiores), the superior medullary velum (velum medullare superius), and the lemniscal triangle (trigonum lemnisci).

The superior medullary velum is a thin sheet of White matter stretched between the superior cerebellar peduncles laterally and the Cerebellum superiorly. Anteriorly, the superior medullary velum attaches to the tectum of the midbrain, where it terminates in the frenulum of the superior medullary velum within the sulcus between the two inferior colliculi. Together with the superior cerebellar peduncles, the superior medullary velum forms the anterosuperior wall of the roof of the Fourth ventricle of the Brain. The lateral Regions of the isthmus of the rhombencephalon contain the lemniscal triangle, which is bounded anteriorly by the brachium of the inferior colliculus, posteriorly and superiorly by the superior cerebellar peduncle, and laterally by the lateral sulcus located on the external surface of the cerebral peduncle. Within the substance of the lemniscal triangle lies the lateral lemniscus (lemniscus lateralis), which constitutes a part of the Auditory pathway.



Last update: 08/08/2026

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