VAGUS NERVE. 709 



vasomotors takes some part in the inflammation, as the hyperemia thus induced 

 affords an inviting field for the complication, (d) Finally, it is still to be determined 

 whether trophic fibers in the vagus subserve the normal preservation of the lung- 

 tissue. According to Michaelson the pneumonia developing immediately after 

 section of the vagus is seated principally in the middle and lower lobes, while the 

 catarrhal inflammation that develops more slowly after section of the recurrent 

 nerves is situated usually in the upper lobes. Rabbits die amid symptoms of pneu- 

 monia as a rule within twenty-four hours; when the precautions mentioned are 

 taken, in the course of several days. Dogs may survive for a considerable time. It 

 is doubtful whether the paralysis of the intra-abdominal fibers of the vagus favors 

 the occurrence of death. In rabbits, extirpation of the ninth, tenth, and twelfth 

 nerves on one side causes death from pneumonia. After section of both vagi in 

 rabbits acute fatty degeneration of the heart and abnormal friability of the smaller 

 coronary vessels develop in consequence of loss of the trophic functions of the 

 vagus. In birds the lungs remain free from inflammation after section of both 

 vagi, because the upper portion of the larynx retains its faculty of reflex closure. 

 Nevertheless, death results in a week from inanition in consequence of paralysis 

 of the crop, in which the food undergoes putrefaction. At the same time the 

 heart is in a state of fatty degeneration, as are also the liver, the stomach, and 

 the muscles. According to Wassilieff the heart exhibits parenchymatous swelling 

 and slight waxy degeneration. In ruminants considerable tympanitic distention 

 of the stomach results, because eructation is impossible. Frogs, which with each 

 inspiration open the glottis, which is closed during rest, die of asphyxia after section 

 of the trunks of the vagi. Section of the pulmonary branches is unattended with 

 injurious effect. If the vagi are divided below the origin of the recurrent nerves 

 the lungs remain healthy in the dog, although disorders of secretion and of the 

 movements of the stomach set in. As a result putrefactive decomposition occurs 

 in the stomach, in consequence of which death takes place. 



The esophageal plexus (r) is formed by branches above from the 

 inferior laryngeal, then from the pulmonary plexus, and below from the 

 trunk of the vagus itself (being derived from the posterior root-fibers 

 of the trunk). The plexus endows the esophagus with motility and with 

 indistinct sensibility (also that of muscular contraction) only in its 

 upper portion and it supplies it with reflex fibers. 



The gastric plexus (o o) consists of the anterior (left) extremity 

 of the vagus, which also sends fibers to the esophagus and passes along 

 the lesser curvature and in part sends fibers through the transverse 

 fissure to the liver. The posterior (right) vagus, after giving off 

 a few fibers to the esophagus, takes part in the formation of the gastric 

 plexus, which receives sympathetic fibers at the pylorus. The vagi 

 supply the stomach with motor fibers, derived from its root (not from 

 the accessory nerve) , and also inhibitory or relaxing fibers for the cardia. 

 Further, the vagus supplies the secretory fibers for the gastric mucous 

 membrane. These contain vasomotor fibers., for division of the trunks 

 of the vagi causes hyperemia of the mucous membrane of the stomach. 

 The gastric fibers, however, receive the centripetal filaments, through 

 which the secretion of saliva is stimulated. Whether also vomiting can 

 be excited through them is still doubtful. 



After section of both vagi below the diaphragm death results, at the latest 

 after an interval of three months, preceded by emaciation, inflammatory altera- 

 tions in the mucous membrane of the stomach and perivascular hyperplasia in the 

 liver and in the kidneys. 



About two-thirds of the right vagus, however, passes at the 

 stomach into the celiac plexus (m) and thence, accompanying the 

 arteries, to the liver, the spleen, the pancreas, the small intestines, the 

 kidneys, and the adrenal glands. The influence of the vagus upon 

 the movements of the intestine has been discussed in the considera- 



