PNEUMOGASTRIC NERVE, or Par Vagum, derives the first of its names from its sup plying th,e lungs and stomach with nervous filaments, and the second from the wander ing course which it pursues. It emerges from the medulla oblongata by eight or ten filaments, which unite and form a flat cord that escapes from the cavity of the cranium (iu association with the glossopharyugeal and spinal accessory nerve) by the jugular foramen. In this foramen it forms a well-marked ganglionic swelling, while another is observed immediately after its exit from the skull. The nerve runs straight down the neck between and in the same sheath as the intwual jugular vein and the carotid artery. Below the root of the neck its course is different on the two sides; the right nerve run ning along the back of the esophagus is distributed to the posterior surface of the stomach, and finally merges into the solar plexus; while the left nerve runs along the front of the esophagus to the stomach, sending branches chiefly over its anterior surface.
From anatomical considerations, based on the distribution of this nerve, and from the results of experiments on animals, it may be concluded that this is a mixed nerve, containing filaments both of sensation and motion. The pulmonary branches exercise a most important influence upon the respiratory acts, for when the pneumogastrics on both sides have been divided above the giving off of the pulmonary branches, the most severe elyspneea comes on, the number of respirations is much diminished, and the ani mal breathes as if it were asthmatic; after a short time the lungs become congested and dropsical, and the bronchial tubes filled with a frothy serous fluid: and if the cut ends of the nerves are kept apart, the animal never survives above three days. The gastric
branches influence the movements of the stomach, while their destruction does not materially affect the secretion of the gastric juice or the process of chyiffication. Loss of voice and difficulty of breathing have been frequently traced to the pressure of an aneurism or other tumor on the recurrent or inferior laryngeal. Whooping-cough is ascribed by many high authorities to an affection of the pneumogastrie nerve; and the violent spasmodic cough which accompanies enlarged bronchial glands is probably due to the irritation of its pulmonary branches. The sympathy which exists between the digestive and the respiratory and circulating organs is explained by the anatomical rela tions of this nerve. For example, both asthma and palpitation of the heart are often to be traced to some deranged state of digestion. Voinitinf may be excited by irritation of the central or the distal extremities of the nerve. In disease of the brain the vomit ing, which is often an early symptom, is caused by irritation of the central extremity; and in sea-sickness it is that extremity also which is irritated by the disturbed state of the circulation in the cranium; while by introducing emetic substances into the stomach the vomitiug is produced by the irritation of the peripheral (or distal) filaments.