Visceral Paths to the Cerebellum, Spinal and Cranial.— Sympathetic impulses from viscera enter the dorsal nucleus (of Clark) in the cord and the dorsal nucleus of the vagus in the medulla. Note first the spinal path. Visceral impulses tra verse the white rami communicantes and the posterior roots of the spinal nerves to the dorsal nucleus of Clark; they ascend to the cerebellar cortex through the dorsal spino-cerebellar tract, which runs along the surface of the cord just dorsal to the mid lateral line, and continues through the restiform body to the cortex of the vermis superior on both sides of the median plane. In the cerebellum impulses are excited that maintain muscle tone and, probably, coordinate viscero-motor, viscero-inhibitory, cardiac accelerator, secretory, trophic, and other sympathetic functions. By which of the familiar cerebello-fugal paths these impulses descend to the intermedio-lateral nucleus of the cord it has not been determined, but they pass down through the lateral funiculus of the cord. Having reached the intermedio lateral nucleus (the visceral efferent nucleus), the impulses continue through the axones of that nucleus to sympathetic ganglia, whose axones complete the path; the axones of the intermedio-lateral nucleus constitute the small fibers in the anterior roots of the spinal nerves and the efferent fibers of the white rami communicantes; axones from the sympathetic gan glia, the post-ganglionic fibers, convey the impulses to their destination, the gland cells and smooth and heart muscles.
The cranial path for visceral impulses is contained chiefly in the vagus nerve. Sympathetic impulses ascend the afferent fibers of the vagus to the terminal part of its dorsal nucleus (nucleus of ala cinerea); they first excite reflex impulses in the efferent part of the dorsal nucleus and, then, proceed through axones of that nucleus (nucleo-cerebellar fibers) to the cere bellar cortex, by way of the restiform body. Cerebellar im pulses coordinating cardiac inhibition, secretion, etc., etc., in the field of the vagus, are returned to the efferent part of the dorsal nucleus through the cortico-nuclear and cerebello-teg mental fibers. Then the vagus carries the impulses to various sympathetic ganglia, whose post-ganglionic fibers bear them on to the gland cells and involuntary muscles innervated through the vagus.