During human
fetal development, the hippocampal sulcus first appears at approximately 10 weeks of
gestational age. At this stage it exists as a broad shallow fissure along the surface of the dentate gyrus. Gradually, the fissure deepens and shifts toward the
cornu ammonis. After about 18 weeks, the walls of the fissure fold into each other and begin to fuse. By 30 weeks, the hippocampal sulcus is normally obliterated except for its most medial part, leaving a shallow surface indentation. ==Clinical significance==