PNEUMOGASTRIC NERVE. 449 



The Muscular branch divides into filaments, which are distributed 

 to the stylo-pharyngeus and to the posterior belly of the digastricus 

 and stylo-hyoideus muscle. 



The Pliarynyeal branches are two or three filaments which are 

 distributed to the pharynx and unite with the pharyngeal branches 

 of the pneumogastric and sympathetic nerve to form the pharyngeal 

 plexus. 



The Lingual branches enter the substance of the tongue beneath the 

 hyo-glossus and stylo-glossus muscle, and are distributed to the mu- 

 cous membrane of the side and base of the tongue, and to the epi- 

 glottis and fauces. 



The Tonsillitic branches proceed from the glosso-pharyngeal nerve 

 near its termination ; they form a plexus (circulus tonsillaris) around 

 the base of the tonsil, from which numerous filaments are given off 

 to the mucous membrane of the fauces and soft palate, communicating 

 with the posterior palatine branches of Meckel's ganglion. 



PNEUMOGASTRIC NERVE (vagus). The pneumogastric nerve arises 

 by ten or fifteen filaments from the groove between the corpus olivare 

 and corpus restiforme, immediately below the glosso-pharyngeal, and 

 passes out of the skull through the inner extremity of the jugular fora- 

 men in a distinct canal of the dura mater. While situated in this 

 canal it presents a small rounded ganglion (ganglion jugulare) ; and 

 having escaped from the skull, a gangliform swelling (plexus gangli- 

 formis), nearly an inch in length, and surrounded by an irregular 

 plexus of white nerves, which communicate with each other, with the 

 other divisions of the eighth pair, and with the trunk of the pneumo- 

 gastric below the ganglion. The plexus gangliformis (ganglion of the 

 superior laryngeal branch, of Sir Astley Cooper), is situated, at first, 

 behind the internal carotid artery, and then between that vessel and 

 the internal jugular vein. The pneumogastric nerve then descends the 

 neck within the sheath of the carotid vessels, lying behind and be- 

 tween the artery and vein, to the root of the neck. Here the course 

 of the nerve at opposite sides becomes different. 



On the right side it passes between the subclavian artery and vein 

 to the posterior mediastinum, then behind the root of the lung to the 

 oesophagus, which it accompanies to the stomach, lying on its posterior 

 aspect. 



On the left it enters the chest parallel with the left subclavian ar- 

 tery, crosses the arch of the aorta, and descends behind the root of the 

 lung, and along the anterior surface of the oesophagus, to the stomach. 



The fibres of origin of the pneumogastric nerve, like those of the 

 glosso-pharyngeal, may be traced through the fasciculi of the corpus 

 restiforme into the grey substance of the floor of the fourth ventricle. 



2 G 



