part of cerebral cortex insular cortex BTO:0001105 BrendaTissueOBO The insula is a portion of the cerebral cortex that is not visible until the margins of the lateral sulcus are opened up, or, as in this case, removed. The insular cortex is roughly triangular. Originally part of the superficial cortex, in higher mammals it became submerged beneath the expanding cortex around it, thereby remaining relatively close to the basal ganglia of the hemisphere. Complete submergence of the insular cortex is a feature of the human brain and is not found even in other primates. insula insular lobe insulary cortex