482 THE NERVOUS SYSTEM. 



spinal accessory takes part in the formation of the pharyngeal plexus 

 supplying the upper constrictor muscles of the pharynx. The process 

 of deglutition, therefore, is excited at its commencement by sensitive 

 impressions conveyed through the glossopharyngeal nerve; but its 

 movements are executed by a reflex impulse transmitted through the 

 motor fibres of several distinct branches of communication. 



Tenth Pair. The Pnenmogastric. 



The pneumogastric nerve, remarkable for its extensive course and 

 varied distribution, has received its name from the two most important 

 organs in which it terminates, namely, the lungs and stomach. It 

 arises from the side of the medulla oblongata by ten or fifteen fila- 

 ments, arranged in linear series continuously with those of the glosso- 

 pharyngeal. Their nucleus of origin is an extended tract of gray sub- 

 stance on the posterior surface of the medulla oblongata, just outside 

 the lower extremity of the fasciculus teres. This deposit, which, by the 

 divergence of the posterior columns, is exposed to view on the floor 

 of the fourth ventricle, is known as the ala cinerea. At its anterior 

 extremity it is continuous with the nucleus of the glossopharyngeal ; 

 and at its posterior extremity it joins that of the spinal accessory. 

 From its deep surface it gives out the root fibres of the pneumo- 

 gastric nerve, which run downward and outward through the medulla, 

 and emerge, in the above mentioned series of filaments, from its lateral 

 surfaceo 



The filaments of the pneumogastric, after leaving the medulla, unite 

 into a trunk which passes out of the cranium by the jugular foramen. 

 Here it presents a ganglionic swelling, known as the "jugular ganglion." 

 At or immediately beyond this situation, the nerve is joined by a motor 

 branch from the spinal accessory ; and it afterward receives similar fila- 

 ments from four other sources ; namely, the facial, the hypoglossal, and 

 the anterior branches of the first and second cervical nerves. 



While passing down the neck the pneumogastric nerve contributes 

 an anastomotic branch to the pharyngeal plexus. Its first important 

 branch of distribution is the superior laryngeal nerve, which pene- 

 trates the larynx by an opening in the thyro-hyoid membrane, and is 

 distributed to the mucous membrane of the epiglottis and the laryngeal 

 cavity. It also gives off a small muscular branch to the inferior con- 

 strictor of the pharynx and to the crico-thyroid muscle of the larynx. 

 It supplies several filaments, which, with others from the great sym- 

 pathetic, form the laryngeal plexus ; and by this plexus it sends fibres 

 to the upper cardiac nerves of the sympathetic. Other filaments which 

 it gives off in the neck also join the cardiac branches of the sympa- 

 thetic, or sometimes, according to Cruveilhier, pass directly to the 

 cardiac plexus beneath the arch of the aorta. 



The next branch is the inferior laryngeal nerve, which separates 

 from the pneumogastric after its entrance into the chest, and ascends, 

 between the trachea and oesophagus, to the larynx, giving off filaments 



