Starting Point: Apex of supramarginal gyrus at the intrapareital, or occasionally at the postcentral sulcus
Direction: Superior to Inferior
Ending Point: End of the sulcus or far enough down to contain the supramarginal gyrus. If it forks at the inferior extent, stop at the intersection.
Notes: It will hug the posterior border of the supramarginal gyrus. Never continue the sulcus all the way to the superior temporal. It is alright to jump a gyrus to get to the primary intermediate sulcus. If, at the inferior portion of the sulcus, you have a choice between moving inferior and moving anterior, move in the anterior direction. If the only way to draw the sulcus is off the post central, then do so. This suclus may not always be present.