Anterior Median Fissure
Extends the entire length of the medulla oblongata and composed or pia mater terminating at the bottom of the pons. Anterior external arcuate fibers extend over the medulla and connect to the inferior penduncle.
Posterior Median Fissure
Exists exclusively in the closed region of the medulla oblongata and terminates in the middle of it where the fourth ventricle begins.