Anterior median fissure of medulla oblongata

The anterior median fissure of medulla oblongata is a prominent fissure located on its ventral surface. This midline fissure runs the entire length of the anterior surface of the medulla. It is bordered on either side by two longitudinal swellings known as the pyramids, which are formed by the aggregation of corticospinal tract fibers. The fissure begins at the lower border of the pons and extends inferiorly, where it seamlessly transitions into the anterior median fissure of the spinal cord’s ventral surface.

In the lower part of the medulla oblongata, the anterior median fissure is marked by an interruption caused by fiber bundles that cross obliquely from one side to the other; this crossing forms what is known as the pyramidal decussation. These fibers belong to the lateral corticospinal tract, which is crucial for motor control. Above the site of the decussation, additional fibers, referred to as the anterior external arcuate fibers, emerge from the anterior median fissure. These fibers curve laterally and posteriorly as they travel along the surface of the medulla oblongata, eventually reaching the cerebellum through the inferior cerebellar peduncle.