The collateral eminence is an elongated swelling lying lateral to and parallel with the hippocampus

Hippocampus

The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

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It corresponds with the medial part of the collateral fissure

Collateral fissure

The collateral fissure is on the tentorial surface of the hemisphere and extends from near the occipital pole to within a short distance of the temporal pole....

, and its size depends on the depth and direction of this fissure.

It is continuous behind with a flattened triangular area, the trigonum collaterale, situated between the posterior and inferior cornua.

It is not always present.