Inferior Frontal Sulcus (#4)
Starting Point: Most posterior segment of the lateral orbital sulcus
Direction: Anterior to Posterior
Ending Point: Pre Central sulcus
Notes: Frequently discontinuous. Always terminates ON Pre Central Sulcus on posterior end even if you have to jump a sulcus that abuts the pre central. Makes an upside-down “Y” with the Pre Central. The sulcus may be divided from Pre Central by pars opercularis and pars triangularis (see Duvernoy 1). Posterior end determined by taking lowest continuous horizontal sulcus coming off the Pre Central. Always take the inferior route at the most anterior intersection. Often terminates at an insular sulcus. Most anterior extent always ends at most anterior vertically oriented sulcus, e.g. lateral orbital sulcus (see Duvernoy 2). At the anterior end, never jump more than one vertically oriented gyrus before taking intersection in the inferior direction (it is often necessary, however, to jump one gyrus). Note, do not chose a sulcus that curves around the inferior surface of the frontal lobe. If it is ambiguous whether you are actually jumping a gyrus, use the slice view to aid you. Anterior end frequently curves back around to move almost posterior in direction.