THE PNEUMOGASTRIC. 559 



plying the mucous membrane of the larynx; the inferior laryngeal 

 branch is a motor nerve, and is essential to the activity of nearly all 

 the muscles of the organ. 



After entering the cavity of the chest, the most important dependency 

 of the pneumogastric nerve is the pulmonary plexus, formed by the 

 separation of the nerve into a considerable number of inosculating 

 branches which send their terminal filaments along the course of the 

 bronchi and their subdivisions, to the ultimate bronchi and lobules of 

 the lungs. In the inferior portion of the chest, the inosculating fila- 

 ments on both sides surround the oesophagus with the cesophageal 

 plexus, from which fibres are supplied to the mucous membrane and 

 muscular coat of this organ. 



The two pneumogastric nerves, after being reconstructed by the union 

 of their branches below the pulmonary plexus, penetrate the cavity of 

 the abdomen and spread out in two sets of gastric branches, which 

 supply the mucous membrane and muscular coat of the stomach. Those 

 belonging to the left pneumogastric nerve supply the anterior wall of the 

 organ, and, extending toward the right as far as the pylorus, send a con- 

 tinuation of nervous filaments to the transverse fissure of the liver, into 

 which they penetrate, together with those of the hepatic plexus of the 

 sympathetic ; those belonging to the right pneumogastric send filaments 

 to the posterior wall of the stomach, and finally communicate with the 

 solar plexus of the sympathetic. 



The pneumogastric nerve, therefore, is distributed, by its various 

 branches, to the mucous membranes and muscular apparatus of the pas- 

 sages by which air and food are introduced into the interior of the body. 

 It also forms connection at several points with branches of the great 

 sympathetic, and, through it, sends fibres to the central organ of the cir- 

 culation, and to the radiating sympathetic plexuses of the abdominal 

 organs. 



Physiological Properties of the Pneumogastric. According to the 

 results obtained by Longet, the pneumogastric is, at its origin, exclu- 

 sively a sensitive nerve. Galvanic irritation applied to the nerve roots, 

 carefully separated from the medulla and from adjacent filaments, was 

 not found to produce any muscular contractions ; but when applied to 

 the trunk of the nerve at a lower level, muscular contractions were 

 readily excited. At this situation the nerve already contains motor 

 fibres derived from inosculation with the spinal accessory, the facial and 

 the hypoglossal, and from the loop of communication between the two 

 upper cervical nerves. In its trunk, accordingly, it has the characters 

 of a mixed nerve, and is capable of providing both for movement and 

 sensibility in the organs to which it is distributed. 



The sensibility of the pneumogastric nerve, however, to mechanical 

 irritation and to painful impressions, is but slightly marked, as shown 

 by the experience of all observers. It may frequently be divided in 

 the middle of the neck in the living, unetherized animal, without any 

 sign of pain being manifested ; and this want of reaction is at times so 



