English: Morphological delineation of the insula and its main structural landmarks in the human and cynomolgus macaque monkey brains. (A,A’) Photographs of the lateral (left) aspect of a human brain with (A) and without (A’) the frontoparietal and temporal opercula that cover the insular cortex, which is located in the depth of the LF. The human insula contains two posterior long posterior gyri (l1 and l2) separated from three anterior short gyri (s1-3) by the central sulcus of the insula (CS). The anterior insula contains an additional accessory short gyrus, which varies in size and demarcation. We consider that this accessory gyrus overlaps with the so-called FI, which is characterized by its high concentration of von Economo neurons (VEN). The insula is delimited by the superior (SPS), inferior (IPS), and anterior (APS) peri-insular sulci. “h” denotes one of the temporal gyri of Heschl. (B–B”) Photographs of the lateral (left) aspect of a cynomolgus macaque monkey brain with (B) and without (B’,B”) the frontoparietal and temporal opercula that cover the insular cortex, which is located in the depth of the LF. The macaque insula is essentially smooth with an incipient ventral gyrus or “mound” and a shallow, but distinct anterior sulci or “ridge,” which marks the limit of the anterior insular region containing the VEN, and which we consider a structural homolog of the human FI.