A number of groups of ganglion cells with special duties are located in the medulla. Those acts which are most important for the execution of the vegetative functions, are arranged and governed by the nerve cells of the medulla. Some of these centres are called automatic, though they are variously affected by many impulses arriving from distant points, while others are purely reflex in their action.

Diagram showing the position of the nuclei of the cranial nerves in the medulla oblongata, etc.

Fig. 252. Diagram showing the position of the nuclei of the cranial nerves in the medulla oblongata, etc., as if seen in antero-posterior section, looking from the median line toward the right side. The nuclei near the median line are more darkly shaded.

Py.Pyramidal tracts; Py Kr, Pyramidal decussation; O, Olivary body; Os, Superior olivary body: V, motor; V', Middle sensory; and V", Lower sensory nuclei of fifth nerve; R v, Roots of fifth nerve; vi, Nucleus of sixth nerve; R vi, Root of sixth nerve; vii, Nucleus; Gf, Knee; and R vii Root of portio dura of seventh nerve; viii, Auditory; ix, Glosso-pharyngeal; x, Vagus; xi, Accessorius; and xii, Hypoglossal nuclei; Rz, Clavate nuclei.

The former are the more essential, and will therefore be first considered.