THE PNEUMOGASTRIC. 557 



Beside the anastomotie branches received by the glossopharyngeal, 

 near its origin, from the facial and the spinal accessory, it also has com- 

 munication with both these nerves near its peripheral distribution. It 

 is joined by a branch of the facial, which accompanies it to the stylo- 

 glossal muscle, and perhaps also to the pillars of the fauces ; and, accord- 

 ing to Cruveilhier, a branch derived from the spinal accessoiy takes 

 part in the formation of the pharyngeal plexus which supplies the upper 

 constrictor muscles of the pharynx. The process of deglutition, there- 

 fore, 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 Pneumogastric. 



The pneumogastric nerve, remarkable for its varied and extensive 

 course and the distribution of its fibres to a number of different locali- 

 ties, has received its name from the two most important organs in which 

 it terminates, the lungs and stomach. It arises from the side of the 

 medulla oblongata by a series of from ten to fifteen separate filaments, 

 arranged in a linear series, continuously with those of the glossopha- 

 ryngeal. The nucleus from which these fibres take their origin is an 

 extended tract of gray matter running in a longitudinal direction 

 along the posterior surface of the medulla oblongata, just outside the 

 lower extremity of the fasciculus teres. This collection of gray matter 

 (Fig. 168, Nu) which is uncovered by the divergence of the posterior 

 columns of the cord, and is thus exposed to view on the floor of the 

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

 tremity it covers, and is continuous with, the nucleus of the preceding 

 nerve, the glossopharyngeal ; and at its posterior extremity it joins 

 that of the following nerve, the spinal accessory. From its deep sur- 

 face it gives out the fibres of origin of the pneumogastric nerve, which 

 run downward and outward through the substance of the medulla, and 

 emerge, as above mentioned, in a series of filaments from its lateral 

 surface. 



The filaments of the pneumogastric, after leaving the side of the 

 medulla oblongata, unite into a single trunk which passes out of the 

 cranium, in company with the glossopharyngeal and the spinal accessory, 

 by the jugular foramen (Fig. 179). Here it presents upon its trunk a gan- 

 glionic swelling, known as the "jugular ganglion." At or immediately 

 beyond the situation of the ganglion, the nerve is joined by an important 

 motor branch of communication from the spinal accessory ; and it after- 

 ward receives filaments 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 takes part, by 

 an anastomotic branch, in the formation of the pharyngeal plexus. Its 

 first important branch of distribution is the superior larynyeal nerve. 



