 The two pyramids contain the motor fibers that pass from the brain to the medulla oblongata and spinal cord.These are the corticobulbar and corticospinal fibers that make up the pyramidal tracts.About 90% of these fibers leave the pyramids in successive bundles and decussate (cross over) in the anterior median fissure of the medulla oblongata as the "pyramidal decussation" or "motor decussation".