Tranverse Occipital Sulcus (#21)
Starting Point: On midline or highest contrast point nearest midline on medial surface of hemisphere. Sulcus frequently branches (y or t intersection) at the midline, stop at the intersection .
Direction: Medial to Lateral
Ending Point: Follow all branches that extend posterior/inferior; insular type sulcus. Stop if you intersect the sulcus lunatus (see Duvernoy, p 16, #11)
Notes: Intraparietal sulcus runs into TOS more than 90 percent of the time. Should start at the most posterior branch at the medial surface (it often forms a Y-intersection with the medial surface of the hemisphere). The sulcus should be continuous and follow all branches that extend posterior/inferior (even if it requires turning medially).