EIGHTH PAIR. 55T 



Its branches of communication are three, and occupy separate grooves on the 

 surface of the promontory. One of these arches forwards and downwards to the 

 carotid canal to join the carotid plexus. A second runs vertically upwards to 

 join the greater superficial petrosal nerve, as it lies in the hiatus Fallopii. The 

 third branch runs forwards and upwards towards the anterior surface of the petrous 

 bone, and passes through a small aperture in the sphenoid and temporal bones, to 

 the exterior of the skull, where it joins the otic ganglion. This nerve, in its course 

 through the temporal bone, passes by the ganglionic enlargement of the facial, and 

 has a connecting filament with it. 



The branches of the glosso-pharyngeal nerve are the carotid, pharyngeal, mus- 

 cular, tonsillitic, and lingual. 



The carotid branches descend along the trunk of the internal carotid artery as 

 far as its point of bifurcation, communicating with the pharyngeal branch of the 

 pneumogastric, and with branches of the sympathetic. 



The pharyngeal branches are three or four filaments which unite opposite the 

 Middle constrictor of the pharynx with the pharyngeal branches of the pneumo- 

 gastric, superior laryngeal, and sympathetic nerves, to form the pharyngeal plexus, 

 branches from which perforate the muscular coat of the pharynx to supply the 

 mucous membrane. 



The muscular branches are distributed to the Stylo-pharyngeus. 



The tonsillitic branches supply the tonsil, forming a plexus (circulus tonsillaris) 

 around this body, from which branches are distributed to the soft palate and 

 fauces, where they anastomose with the palatine nerves. 



The lingual branches are two in number ; one supplies the mucous membrane 

 covering the surface of the base of the tongue, the other perforates its substance, 

 and supplies the mucous membrane and papilla of the side of the organ. 



(2.) PNEUMOGASTRIC OR PAR YAGUM NERVE. 



The PNEUMOGASTRIC NERVE (nervus vagus or par vagum), one of the three 

 divisions of the eighth pair, has a more extensive distribution than any of the 

 other cranial nerves, passing through the neck and cavity of the chest to the upper 

 part of the abdomen. It is composed of both motor and sensitive filaments. It 

 supplies the organs of voice and respiration with motor and sensitive fibres, and 

 the pharynx, oesophagus, stomach, and heart with motor influence. Its superficial 

 origin is by eight or ten filaments from the lateral tract immediately behind the 

 olivary body, and below the glosso-pharyngeal ; its fibres may, however, be traced 

 deeply through the fasciculi of the medulla, to terminate in a gray nucleus near 

 the lower part of the floor of the fourth ventricle. The filaments become united, 

 and form a flat cord, which passes outwards across the flocculus to the jugular 

 foramen, through which it emerges from the cranium. In passing through this 

 opening, the pneumogastric accompanies the spinal accessory, being contained in 

 the same sheath of dura mater with it, a membranous septum separating it from 

 the glosso-pharyngeal, which lies in front. The nerve in this situation presents a 

 well-marked ganglionic enlargement, which is called ganglion jugulare or the 

 ganglion of the root of the pneumogastric ; to it the accessory part of the spinal 

 accessory nerve is connected. After the exit of the nerve from the jugular 

 foramen, a second gangliform swelling is formed upon it, called the ganglion infe- 

 rius or the ganglion of the trunk of the nerve; below which it is again joined by 

 filaments from the spinal accessory nerve. The nerve descends the neck in a straight 

 direction within the sheath of the carotid vessels, lying between the internal caro- 

 tid artery and internal jugular vein as far as the thyroid cartilage, and then be- 

 tween the same vein and the common carotid to the root of the neck. Here the 

 course of the nerve becomes different on the two sides of the body. 



On the right side, the nerve passes across the subclavian artery between it and 

 the subclavian vein, and descends by the side of the trachea to the back part of the 

 root of the lung, where it spreads out in a plexiform network (posterior pulmonary), 



