Fig 2.

The transverse gyrus and the orbitofrontal insula relationship. Base view of the orbital surface of the left frontal lobe after resection of part of the gyrus rectus (GR) and the anterior portion of the temporal lobe (T). Medial is to the reader’s left. I indicates olfactory bulb; II, optic chiasm and tract. The H-shaped orbital sulcus (arrowheads) defines the MOG, POG, anterior orbital gyrus (AOG), and lateral orbital gyrus (LOG). At the posteromedial aspect of the orbitofrontal surface, the posterior portion of the MOG merges with the medial portion of the POG to form the prominent PMOL. PMOL gives rise to the transverse insular gyrus (t) that extends laterally to form the pole (po) of the insula just anteroinferomedial to the apex (asterisk) of the insula. The CS (dashed line) curves inferiorly immediately behind and below the apex and the pole en route to join the stem of the sylvian fissure. The ASG (a) and the PSG (p) converge to form the apex of the insula anterior to the CS. In this image, the deliberate slight rotation used to illustrate the course of the transverse gyrus from the PMOL to the pole also rotates the apex medially, so the apex does not appear to lie as far lateral in position as it would in a true base view.