Experimental and Anatomical Studies on the Vagus Nerve of the Cat

Abstract

Since Ranson and his associates 1 , 2 have demonstrated that the rootlets of the vagus nerve of the dog and the cat are of 2 anatomical types, one resembling the ventral, the other the dorsal roots of thoracic spinal nerves, it seemed desirable to ascertain whether a like differentiation exists in their intramedullary courses. The rootlets of the right vagus nerve were sectioned intracranially in 2 cats and the right nodose ganglion removed in 5 others. After 14 days each animal was killed and the brain stem and cervical cord were fixed in Miiller's fluid. Later they were stained by the method of Marchi. Nearly complete series of sections of the pons and medulla oblongata were mounted.∗

In such histologic preparations there are 3 types of rootlets. The majority of the degenerated myelinated fibers with cell bodies in the jugular and nodose ganglia enter the medulla by way of the upper (cephalic) rootlets, pass over or through the dorsal portion of the descending trigeminal tract and nucleus, then course dorsal to the motor fascicles of the vagus, and ultimately enter the lateral or ventral portion of the solitary bundle. Probably these coarse fascicles (accompanied by no discernible undegenerated fibers) represent an intramedullary continuation of the pure sensory type seen peripherally by Ranson. Medium sized motor bundles can be traced from the dorsal motor nucleus of the vagus, ventral to the tractus solitarius, through the middle or ventral portion of the spinal nucleus of the trigeminal nerve to the surface of the medulla. Many of these motor fibers proceed peripherally through the lower (caudal) group of rootlets. Finally, coursing with certain motor fascicles are smaller groups of degenerated fibers which leave the efferent bundles in a situation ventral to the solitary tract, turn abruptly dorsalward and enter the latter.