Answer. Pars marginalis of the cingulate sulcus.
Brief Discussion
The pars marginalis of the cingulate sulcus is a key structure for secondary identification of adjacent sulci, including the central sulcus. A large number of signs related to the intrinsic features of the pars marginalis of the cingulate sulcus as well as the relationship to adjacent sulci have been described. Examples of such signs include the pars mustache signs, anterior shift sign, pars bracket sign, and bifid postcentral sulcus sign.