PNEUMOGASTRIC NERVE, the vagus, or 10th cranial nerve (see CRANIAL NERVES), the lung-stomach nerve. It is formed by the junc tion of from 10 to 15 filaments which arise in the medulla oblongata. They form a flattened band which passes out through the skull with other nerves and pursues its course down the neck behind the carotids, being in the same sheath. Below the clavicle the right and left pneumogastrics go in different directions. The right pneumogastric enters the chest-cavity in front of the subclavian artery, gains the back part of the root of the right lung, breaks up into a coarse series of branches, being joined by the sympathetic, and forms the posterior pulmonary plexus. From this two cords of nerve-tissue continue downward on the right side of the oesophagus. An cesophageal plexus is formed about this tube, into which fibres from both sides enter. The fibres then converge to form a single trunk; this passes through the diaphragm and spreads out on the posterior surface of the stomach. The left pneumogastric passes into the thorax between the left common carotid and left subclavian arteries. It forms a plexus for the left lung corresponding with the right side. Its terminal branch passes in front of the oesophagus, and is finally distributed to the front portion of the stomach. The nerve contains both sensory and motor fibres and its function is complex. It is concerned in the functions of the lower part of the oesophagus. It is the important nerve of respiration; is the great cardiac regulator; and is the chief motor nerve of the stomach.
Diseases of the pneumogastric are compara tively rare, but by reason of its wide distribu tion, and because many of its fibres are dis tributed to a great number of structures, partial affections are not uncommon. The pharyngeal
branches are occasionally involved in diphtheria and in nuclear disease. The pharynx becomes immovable and anaesthetic. Food may lodge in the gullet or enter the windpipe, causing cough ing and strangling. Sometimes fluids regurgi tate through the nose. In the larynx paralysis of the fibres may produce a confusing series of symptoms, with cough, diminution or loss of voice, hoarseness, impairment of respiration, pain, etc. The specialist is alone able to deter mine which branches are involved. Affections of the pulmonary branches affect the nutrition of the lung, pneumonia usually' resulting from destruction of the vagus. Protracted hiccough is an affection of the vagus, as is also bronchial asthma. Unusual rapidity of the heart action (tachycardia) is due to temporary loss of con trol of the vagus on the heart. Cardiac palpita don is due to much the same agency; it is fre quently associated with impaired stomach func tions and is very frequent in hysterical and neurasthenic affections. An abnormally slow pulse (bradycardia) is usually due to an excess of stimulation of the vagus. Angina pectoris (q.v.) is a severe and usually fatal affection im plicating the pneumogastric nerve. The involve ment of the gastric branches may result either in loss of motion or sensation or excess of each. Sobbing and vomiting are largely induced by excessive irritability of the Irwin. Gastralgia is also associated with disorder in this nerve. Loss of function may result in serious impair ment of motion and secretion, although the sympathetic nervous system makes an important part of the nervous supply of the stomach. See HEnar; STOMACH. And consult works referred to under these articles.