Sulcal fundi are 3D curves that lie in the depths of the cerebral cortex and are often used as landmarks for downstream computations in brain image processing. In this talk, a sequence of geometric algorithms is introduced to automatically extract the sulcal fundi from magnetic resonance images (MRI) and represent sulcal fundi as smooth polylines lying on the cortical surface. The automatic sulcal extraction can improve the quality and reproducibility of the process as well as yielding considerable time savings. This makes the large number of high-resolution MRI datasets available for analysis.