vermis

The vermis is the narrow, worm‑like median portion of the cerebellum that lies along the midline between the two cerebellar hemispheres. It extends along the superior and inferior surfaces and is connected to the hemispheres by the cerebellar peduncles. The vermis includes regions corresponding to the anterior and posterior vermis and houses parts of the deep cerebellar nuclei, notably the fastigial nucleus.

Functionally, the vermis coordinates axial posture and gait. It integrates sensory input from the spinal cord and vestibular system and transmits processed signals to brainstem centers, supporting balance, trunk control, and proximal limb movements. Subregions contribute to eye movements and head–neck coordination as well.

Clinical significance centers on the effects of vermian injury or atrophy. Lesions produce truncal ataxia, a wide-based unsteady gait, titubation (trunk tremor), and abnormalities of eye movements. Vermian disorders may arise from midline cerebellar tumors such as medulloblastoma in children, as well as from neurodegenerative ataxias and other processes that affect the cerebellar midline.

Etymology and related terms: The name vermis comes from Latin vermis, meaning worm. This root appears in other anatomical terms describing worm-like structures, such as the vermiform (worm-shaped) appendix.