Pyramids - definition
AKA medullary pyramids, fiber bundles in the medulla that appear triangular in cross-section and contain motor fibers, the majority of which are part of the corticospinal tract. These motor fibers decussate at the base of the pyramids in the pyramidal decussation.
2-Minute Neuroscience: Medulla Oblongata
Know Your Brain: Medulla Oblongata