The two pyramids contain the motor fibers that pass from the brain to the medulla oblongata and medulla spinalis, corticobulbar and corticospinal fibers.

When these pyramidal fibers are traced downward, it is found that some two-thirds 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.

Having crossed the middle line, they pass down in the posterior part of the lateral funiculus as the lateral cerebrospinal fasciculus.

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  Diagrams of the medulla spinalis.
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  Medulla oblongata and pons. Anterior surface.
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  Decussation of pyramids. Scheme showing passage of various fasciculi from medulla spinalis to medulla oblongata.
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  Section of the medulla oblongata through the lower part of the decussation of the pyramids
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  Section of the medulla oblongata at the level of the decussation of the pyramids.
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  Superficial dissection of brain-stem. Ventral view.
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  The motor tract.

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