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Section of the medulla oblongata at the level of the decussation of the pyramids. (Testut.) 1. Anterior median fissure. 2. Posterior median sulcus. 3. Motor roots. 4. Sensory roots. 5. Base of the anterior column, from which the head (5’) has been detached by the lateral cerebrospinal fasciculus. 6. Decussation of the lateral cerebrospinal fasciculus. 7. Posterior columns (in blue). 8. Gracile nucleus.