Collateral trigone

The collateral trigone is an elevation forming the floor of the atrium and the occipital horn of the lateral ventricle. It is the posterior continuation of the collateral eminence and is produced by an inward impression of the collateral sulcus on the ventricular wall.

In the atrium, the collateral trigone forms the floor, while the adjacent medial wall is shaped by the calcar avis (produced by the calcarine sulcus) and the bulb of the corpus callosum, which contains fibres of the forceps major (originating from the splenium of corpus callosum). The Figure 2 in the article referenced, demonstrates these relationships on a coronal MR image and corresponding anatomical illustration.