Medical Definition of pyramid
1: a polyhedron having for its base a polygon and for faces triangles with a common vertex
2: an anatomical structure resembling a pyramid: asa: renal pyramidb: either of two large bundles of motor fibers from the cerebral cortex that reach the medulla oblongata and are continuous with the corticospinal tracts of the spinal cordc: a conical projection making up the central part of the inferior vermis of the cerebellum
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