Secondary fissure

The secondary fissure (Postpyramidal fissure) of the cerebellum is a prominent anatomical landmark that separates the uvula (lobule IX) from the pyramid (lobule VIII) on the vermis of the cerebellum. It is one of the major fissures used to divide the cerebellum into its constituent lobules.

Anatomical Details

The secondary fissure is located on the inferior (posterior) surface of the cerebellum. In the classical lobular classification system described by Larsell, it serves as the boundary between:

• Lobule VIII (pyramis/biventral lobule) — superior to the fissure

• Lobule IX (uvula/tonsil) — inferior to the fissure

On the cerebellar hemispheres, this fissure separates the biventral lobule (HVIII) from the tonsil (HIX).

Functional and Developmental Significance

The secondary fissure is one of the earliest fissures to appear during cerebellar development, along with the primary fissure and the posterolateral fissure. These three fissures are considered the most consistent and deepest landmarks of the cerebellum, making them reliable reference points in neuroanatomy and neuroimaging.

From a functional standpoint, the regions separated by the secondary fissure belong to the posterior lobe of the cerebellum (also called the "neocerebellum"), which is primarily involved in the coordination of voluntary movements, motor planning, and cognitive functions.