786 THE NEEYOUS SYSTEM. 



Branches and Communications of the Petrous Ganglion. N. Tympanicus. The 

 tympanic branch is the most important offset from this ganglion. It passes 

 through a small canal in the bridge of bone between the jugular foramen 

 and the carotid canal to reach the cavity of the tympanum, where it breaks up into 

 branches, to form, along with branches from the carotid plexus of the sympathetic 

 on the internal carotid artery (nn. caroticotympanici superior et inferior, O.T. small 

 deep petrosal), the plexus tympanicus Jacobsoni (tympanic plexus), for the supply of 

 the mucous lining of the tympanum, mastoid cells, and auditory tube (Fig. 656, 

 p. 782). The fibres of the tympanic branch of the glossopharyngeal nerve 

 become reunited to form, by their union with a small nerve from the genicular 

 ganglion of the facial nerve (anastomotic with the tympanic plexus), the lesser super- 

 ficial petrosal nerve in the substance of the temporal bone. This passes forwards 

 through the temporal bone, and eventually joins the otic ganglion. 



Besides forming the tympanic branch, the petrous ganglion of the glossopharyngeal 

 nerve communicates with three other nerves (1) with the superior cervical ganglion of 

 the sympathetic ; (2) with the auricular branch of the vagus ; and (3) sometimes with 

 the jugular ganglion of the vagus. 



In the neck the glossopharyngeal nerve gives off two branches. (1) As it crosses 

 over the stylopharyngeus muscle it supplies the nerve to that muscle (ramus stylo- 

 pharyngeus), fibres of which pierce the muscle to reach the mucous membrane of 

 the pharynx. (2) Kami Pharyngei. The pharyngeal branches of the nerve supply 

 the mucous membrane of the pharynx directly after piercing the superior constrictor 

 muscle, and indirectly after joining, along with the pharyngeal offsets from the 

 vagus and the superior cervical ganglion of the sympathetic, in the formation of 

 the pharyngeal plexus. 



The terminal branches of the nerve supply the mucous membrane of the 

 tongue and adjacent parts. Kami Tonsillares. A tonsillar branch forms a plexus 

 to supply the mucous membrane covering the palatine tonsil, the adjacent part of 

 the soft palate, and the palatine arches. Kami Linguales. Lingual branches supply 

 the mucous membrane of the dorsal third and lateral half of the tongue, extending 

 backwards to the glosso-epiglottic folds and the front of the epiglottis. 



NERVUS VAGUS. 



The tenth or vagus nerve (O.T. pneumogastric) arises from the brain by 

 numerous fila radicularia attached to the floor of the postero-lateral sulcus of the 

 medulla oblongata, in series with the glossopharyngeal nerve above and the accessory 

 nerve below it (for the deep connexions, see p. 656). The fila of the nerve unite 

 to form a single trunk which emerges into the neck through the jugular foramen. 



In the jugular foramen the nerve occupies the same sheath of dura mater as the 

 accessory nerve, it is placed behind the glossopharyngeal nerve, and a small 

 ganglion the jugular ganglion is developed upon it. 



In the neck the vagus nerve pursues a vertical course in~ front of the vertebra] 

 column. It occupies the carotid sheath, lying between and behind the internal and 

 common carotid arteries and the internal jugular vein. It enters the thorax behind 

 the large veins : on the right side, after crossing over the subclavian artery; on the 

 left side, in the interval between the left common carotid and subclavian arteries. 

 In the upper part of the neck, immediately below the jugular foramen, a second and 

 larger ganglion the ganglion nodosum is developed on the trunk of the nerve. 



In the thorax the nerves occupy the superior and posterior mediastinal spaces, 

 and their relations are different on the two sides, (a) In the superior mediastinum 

 the right nerve continues its course alongside the innominate artery and the trachea, 

 and behind the right innominate vein and superior vena cava, to the posterior 

 surface of the root of the lung. The left nerve courses downwards between the 

 left common carotid and subclavian arteries, and behind the left innominate vein 

 and the phrenic nerve. It passes over the aortic arch, and then proceeds to the 

 posterior surface of the root of the left lung. (&) In the posterior mediastinum t 

 vagi nerves are concerned in the formation of two great plexuses the pulmonar) 

 and the cesophageal. Behind the root of each lung the nerve breaks up to fonr 



