_Hight vagus.—As the right vagus is entering the abdomen it sends numerous branches upon the posterior part of the termination of the cesophagus and of the cardiac extremity of the stomach. Part of these disappear in the mus cular fibres of the cesophagus and stomach ; others anastomose with the branches of the left vagus, while others proceed downwards and to the left side upon the posterior surface of the large cul-de-sac of the stomach, sending fila ments into the muscular coat, and also anas tomosing with the filaments of the splenic plexus accompanying the vase brevia. The right vagus also sends some branches upon the posterior surface of the stomach, to be distri buted in that part of the organ, a few of which proceed as far as the large curvature, and course along it from left to right. It also sends two or three branches along the smaller curvature, which anastomose with the coronary plexus and branches of the left vagus. A considerable portion of the right vagus,—so large as generally to present the appearance of being the continuation of the trunk of the nerve,—proceeds from the postetior surface of the cardiac region of the stomach, backwards and downwards to the left side of the cceliac axis, sending branches to the splenic, the coro nary, and to the superior mesenteric plexuses, to the plexus surrounding the pancreatic branches of the splenic artery; and it ultimately termi nates in the left semilunar ganglion.. The branches of the right vagus running upon the posterior surface of the lower part of the cesophag,us and cardiac orifice of the stomach have been termed the posterior cardiac plexus.t Dr. Remak has discoveied numerous small ganglia upon the filaments of the cardiac nerves, as they are ramified upon the surface of the heart;/ also upon some of the filaments of the pulmonary plexus, and upon some of the finer branches of the superior laryngeal nerve.§ These ganglia can scarcely be seen by the naked eye, and it is only when examined by the microscope that we can satisfactorily determine their nature. These ganglia appear to be placed upon the filaments of the sympa thetic, conjoined with the branches of the vagi, and not upon those of the vagi.
According to Volkmann and Bidder the vagus oerve contains, in all vertebrated animals, a greater number of sympathetic than cerebro spinal filaments; and this preponderance of the sympathetic over the cerebro-spinal is more rnarked in the lower than in the higher verte brate. This remark is in conformity with the observations of E. II. Weber upon the relative size of the vagus and sympathetic in the diffe rent families of the vertebrate, from which it appears that in the lower vertebrate the vagus increases, the sympathetic diminishes, in size. The branches of the vagus distributed in the cesophagus, heart, lungs, stomach, liver, and gills, are chiefly composed of sympathetic filaments, while the recurrent one of the motor branches is chiefly composed of cerebro-spinal filaments.* Connection of tke vagus and spinal accessory. We have seen that, as the vagus and accessory emerg,e from the fommen lacerum posterius, the intemal branch of the accessory joi»s itself to the vagus, and that while part of its filaments go to assist in forming the superior pharyngeal branch of the vagus, the rest pro ceed downwards with the trunk of the vagus, and become incorporated with it. Bischoff statest that he has not been able to trace the filaments of the accessory into any of the branches of the vagus except the pharyngeal, while Bendz I has been more successful. Ile
states that the portion of the accessory which accompanies the vagus down the neck sends a few filaments to the upper part of the inferior ganglion of the vagus, and then joins itself to some of the posterior and external fibres of the vagus which do not pass through the ganglioo. Below the ganglion these fibres form part of the trunk of the nerve, being enclosed in tlie same neurilema with those which pass through the ganglion. At the lower edge of the gan glion, or sometimes a little lower, the accessory portion sends off some filaments which often join the external branch of the superior laryn geal, but more frequently give twigs to the stemo-thyroid muscle. Other fibres of thei accessory portion accompany the vagus into the' thorax, and some of them assist in forming the recurrent nerve. Some small twigs from tlR accessory join the pulmonary and cardiac plex uses ; the remainder accompany the vagus to the stomach, where they are lost. Mr. Spence states that those fibres of the vagus which do not pass through the superior ganglion are joined by the internal branch of the accessory ; and that these together form a small flat band which may be tmced among the other fibres o the vagus to the lower part of the neck, where it is joined by some of the other fibres of thi vagus which have passed through the ganglion, and seems to go principally to the formation o the recurrent nerve.
We have seen that the vagi are distributed over a large space and upon many organs. They send branches to the external ear, to the pharynx, the larynx, the cesophagus, the trachea, the thyroid body, the heart, the lungs, the stomach ; also to the liver, the spleen, the pancreas, the small intestines, and probably to other viscera of the abdomen. In their course they communicate very freely and extensively with the sympathetic,§ and to a greater or less extent with several of the other cerebro-spinal nerves, as the spinal accessory, the glosso pharyngeal, the hypo-glossal, the portio dura, the two superior cervical, and sometimes with some of the lower cervicals. The vagi are very extensively ramified upon the internal tegumentary membrane, as the mucous mem brane of the pharynx, larynx, cesophagus, sto mach, trachea, and lungs, and send only one small branch, viz. the ramus auricularis, to the external tegumentary membrane. Many of its branches are distributed upon the mus cular fibres surrounding the tipper part of the digestive and respiratory tubes.
Physiology y. the nervus vagus.—From the distribution of this nerve in so many of the most important organs in the body which it is impossible to insulate, or prevent their mutual actions and reactions upon each other, and from its numerous and intimate connections with several other nerves, investigations into its physiology are beset with unusual difficulties. As, however, its lesions are attended by the most serious derangements of the respiratory and digestive organs, and as a knowledge of its functions bears in a prominent manner upon many interesting questions both in special and general physiology, it has naturally attracted the frequent attention of the physiologist, and has been made the subject of numerous experi mental investigations.