decussation of the pyramids

Intercrossing of fibers of the corticospinal tract in the lower medulla oblongata. Pathology: - crossing of corticospinal tract fibers accounts for the observation that lesions in the corticospinal tract above the medulla or lesions in the motor cortex result contralateral hemiplegia

References

Stedman's Medical Dictionary 27th ed, Williams & Wilkins, Baltimore, 1999