Its lower part is interrupted by bundles of fibers that cross obliquely from one side to the other, and constitute the pyramidal decussation.

Most of the corticospinal fibers (about 80%) cross over to the contralateral side in the medulla oblongata (pyramidal decussation).

It is formed by approximately 2% of the corticospinal fibers that do not cross to the opposite side of the brainstem in the pyramidal decussation.

It controls fine movement of ipsilateral limbs (albeit contralateral to the corresponding motor cortex) as it lies distal to the pyramidal decussation.

After crossing over to the contralateral side in the medulla oblongata (pyramidal decussation), the axons travel down the spinal cord as the lateral corticospinal tract.

When these pyramidal fibers are traced downward, it is found that some three-fifths or more of them leave the pyramids in successive bundles, and decussate in the anterior median fissure of the medulla oblongata, forming what is termed the pyramidal decussation or motor decussation.