788 THE NERVOUS SYSTEM. 



the large posterior pulmonary plexus, from the lower end of which two nerves 

 emerge on each side. These nerves on the right side pass obliquely over the vena 

 azygos; on the left side they cross the descending thoracic aorta. Both series 

 reach the oesophagus, and divide into small anastomosing branches which form the 

 cesophageal plexus. At the oesophageal opening of the diaphragm the two nerves 

 become separated from the plexus, and entering the abdomen the left nerve in 

 front of the oesophagus, the right nerve behind it they terminate by supplying 

 the stomach and other abdominal organs. 



The communications and branches of the vagus nerve may be described as 

 (i.) ganglionic, (ii.) cervical, (iii.) thoracic, and (iv.) abdominal (Fig. 660). 



Ganglion Jugulare. The jugular ganglion (O.T. ganglion of the root) is small 

 and spherical. It occupies the jugular foramen, and gives off two branches 

 meningeal and auricular. 



Ramus Meningeus. The meningeal branch passes backwards to supply the 

 dura mater of the posterior fossa of the skull. 



Ramus Auricularis. The auricular branch ascends to the ear in a fissure 

 between the jugular and stylo-mastoid foramina. It receives near its origin a twig 

 from the tympanic branch of the glossopharyngeal nerve, and usually communi- 

 cates with the facial nerve by a branch arising from the latter in the canalis 

 facialis. The nerve is distributed to the back of the auricle and the external 

 acoustic meatus, and communicates superficially with the posterior auricular nerve. 



Communications. Besides supplying the meningeal and auricular branches, this 

 ganglion receives communications from (1) the superior cervical ganglion of the 

 sympathetic ; (2) the accessory nerve ; and (3) (sometimes) the petrous ganglion of the 

 glossopharyngeal nerve {ramus anastomoticus cum nervo glossopharyngeo}. 



Ganglion Nodosum. The ganglion node-sum (O.T. ganglion of the trunk), 

 placed immediately below the preceding, is large and fusiform. Like the jugular 

 ganglion, it supplies two branches the pharyngeal and superior laryngeal nerves. 



Rami Pharyngei. The pharyngeal branch receives its fibres (through the 

 ganglion) from the accessory nerve. It passes obliquely downwards and medially 

 to the pharynx between the internal and external carotid arteries, and combines with 

 the pharyngeal branches from the glossopharyngeal and superior cervical ganglion 

 of the sympathetic to form the pharyngeal plexus. From this plexus the muscles of 

 the pharynx and soft palate (except the stylopharyngeus and tensor veli palatini) 

 are supplied. The lingual branch is a small nerve which separates itself from the 

 plexus and joins the hypoglossal nerve in the anterior triangle of the neck. 



N. Laryngeus Superior. The superior laryngeal nerve passes obliquely down- 

 wards and medially, medial to the external and internal carotid arteries, towards 

 the thyreoid cartilage. It divides in its course into two unequal parts a larger 

 internal and a smaller external laryngeal branch. 



Ramus Internus. The internal laryngeal branch passes medially into the 

 larynx between the middle and inferior constrictor muscles of the pharynx and 

 through the thyreo-hyoid membrane. It supplies the mucous membrane of the 

 larynx, reaching upwards to the epiglottis and base of the tongue, and forms com- 

 munications beneath the lamina of the thyreoid cartilage with the branches of the 

 inferior laryngeal nerve (ramus anastomoticus cum nervo laryngeo inferiore). 



Ramus Externus. The external laryngeal branch passes downwards upon the 

 inferior constrictor muscle of the pharynx. It supplies branches to that muscle, 

 and ends in the crico-thyreoid muscle. 



Communications. Besides supplying these pharyngeal and laryngeal nerves, this 

 ganglion has the following communications with other nerves: (1) with the superior 

 cervical ganglion of the sympathetic ; (2) with the hypoglossal ; (3) with the loop 

 between the first and second cervical nerves ; and (4) with the accessory nerve. This 

 nerve applies itself to the ganglion, and thereby supplies to the vagus nerve the inhibitory 

 fibres for the heart, as well as the motor fibres for the pharynx, oesophagus, stomach 

 and intestines, larynx and respiratory organs. 



Branches of the Vagus in the Neck. In the neck the vagus nerve 



