Sulcus limitans

In the fourth ventricle, the sulcus limitans forms the lateral boundary of the medial eminence. In the superior part of the rhomboid fossa, it corresponds with the lateral limit of the fossa and presents a bluish-gray area, the locus ceruleus (which owes its color to an underlying patch of deeply pigmented nerve cells, termed the substantia ferruginea).

It is seen as slight depressions separating the basal and alar plates.