CRANIAL NERVES. 205 



Tenth Nerve. Pneumogastric. Vagus. 



Origin. From the nerve-cells situated along the trunk of the nerve near 

 the medulla oblongata viz.: the jugular and the plexiform ganglia. From 

 the nerve-cells in these ganglia a short process emerges which soon divides 

 into two branches one of which passes centrally, the other peripherally. 

 The central branches enter the medulla oblongata, where they terminate 

 around nerve-cells; the peripheral branches collectively form the main portion 

 of the trunk of the nerve. 



The pneumogastric also contains efferent fibers which have their origin in 

 nerve-cells beneath the floor of the medulla oblongata. It also receives 

 motor fibers from the spinal accessory, the facial, the hypoglossal and the 

 anterior branches of the two upper cervical nerves. 



Distribution. As the nerve passes down the neck it sends off the follow- 

 iny main branches: 



1. Pharyngeal nerves, which assist in forming the pharyngeal plexus, which 

 is distributed to the mucous membrane and to the muscles of the pharynx. 



2. Superior laryngeal nerve, which enters the larynx through the thyrohyoid 

 membrane, and is distributed to the mucous membrane lining the interior 

 of the larynx, and to the cricothyroid muscle and the inferior constrictor of 

 the pharynx. The "depressor nerve," found in the rabbit, is formed by 

 the union of two branches, one from the superior laryngeal, the other from 

 the main trunk; it passes downward to be distributed to the heart. 



3. Inferior laryngeal, which sends its ultimate branches to all the intrinsic 

 muscles of the larynx except the cricothyroid, and to the inferior constrictor 

 of the pharynx. 



4. Cardiac branches given off from the nerve throughout its course which 

 unite with the sympathetic fibers to form the cardiac plexus, to be distrib- 

 uted to the heart. 



5. Pulmonary branches, which form a plexus of nerves, and are distributed to 

 the bronchi and their ultimate terminations, the lobules and air cells. 

 From the right pneumogastric nerve branches are distributed to the 



mucous membrane and the muscular coats of the stomach and intestines, 

 and to the liver, spleen, kidneys, and suprarenal capsules. 



Properties. At its origin the pneumogastric nerve is sensory, as shown 

 by direct irritation or galvanization, though its sensibility is not very marked. 

 In its course it exhibits motor properties, from anastomosis with motor nerves. 



The pharyngeal branches assist in giving sensibility to the mucous membrane 

 of the pharynx, and influence reflex phenomena of deglutition through motor 

 fibers which they contam in, derived frothe spinal accessory. 



