The medulla is the hindmost portion of the vertebrate brain and the most caudal segment of the brainstem. It contains major ascending and descending fiber tracts, cranial nerve nuclei, and centers that mediate the control of vital autonomic functions.
As the lowermost segment of the three-part brainstem, the stalklike medulla is connected rostrally by the pons to the midbrain. At the level of the foramen magnum, it merges caudally with the spinal cord. Sulci and fissures on the surface of the cord extend rostrally over the medulla. Ventrally, the anterolateral sulcus separates the pyramids (medial) from the olivary bodies (lateral). The medulla is divided into two portions, open and closed, as determined by its relationship with the fourth ventricle. The dorsal aspect of the rostral medulla, the open portion, partially encloses the fourth ventricle. The closed medulla is located caudally below the level of the obex...