The collateral fissure is a large sulcus on the tentorial surface of the cerebral hemisphere and extends from near the occipital pole to within a short distance of the temporal pole. It is also known as the medial occipitotemporal sulcus.

Behind, it lies below and lateral to the calcarine fissure, from which it is separated by the lingual gyrus; in front, it is situated between the parahippocampal gyrus and the anterior part of the fusiform gyrus.

This article incorporates text in the public domain from page 820 of the 20th edition of Gray's Anatomy (1918)