The red arrow, a, a’, indicates the course the lateral cerebrospinal fasciculus takes at the level of the decussation of the pyramids; the blue arrow, b, b’, indicates the course which the sensory fibers take.
The posterior median sulcus of medulla oblongata (or posterior median fissure or dorsal median sulcus) is a narrow groove; and exists only in the closed part of the medulla oblongata; it becomes gradually shallower from below upward, and finally ends about the middle of the medulla oblongata, where the central canal expands into the cavity of the fourth ventricle.
