Uncus

The anterior extremity of the hippocampal gyrus is recurved in the form of a hook, the uncus, which is separated from the apex of the temporal lobe by a slight fissure, the incisura temporalis.

Although superficially continuous with the hippocampal gyrus, the uncus forms morphologically a part of the rhinencephalon.

The term uncus was coined by Felix Vicq d’Azyr (1748–1794).

Clinical significance
The part of the olfactory cortex that is on the temporal lobe covers the area of the uncus, which leads into the two significant clinical aspects of the uncus: uncinate fits and uncal herniations.


 * Seizures, often preceded by hallucinations of disagreeable odors, often originate in the uncus.


 * In situations of tumor, hemorrhage, or edema, increased volume of the temporal lobe can push the uncus against the brainstem and its corresponding cranial nerves. If the uncus becomes herniated the structure lying just medial to it, cranial nerve III, can become compressed.  This causes problems associated with a non-functional or problematic CNIII - pupil on ipsilateral side fails to constrict to light, etc. Brainstem damage is typically contralateral to the herniation.