THE VAGUS NERVE 805 



hyoid bone and concurs with the pharyngeal branches of the vagus and with sym- 

 pathetic filaments in forming the pharyngeal plexus; from this branches pass to 

 the muscles and mucous membrane of the pharynx. 



The lingual branch (R. lingualis) is the continuation of the trunk (Fig. 562). 

 It runs along the posterior border of the great cornu of the hyoid bone in front of 

 the external maxillary artery, and dips under the hyo-glossus muscle. It gives 

 collateral branches to the soft palate, isthmus faucium, and tonsil, and ends in 

 the mucous membrane of the posterior part of the tongue, where it supplies gusta- 

 tory fibers to the vallate papillae. A considerable branch unites mth a twig from 

 the lingual nerve. 



The glosso-pharjTigeal is a mixed nerve, containing both motor and sensory fibers. The 

 latter constitute the bulk of the nerve and include those which mediate the special sense of taste. 

 They are processes of the cells of the petrous ganglion. The central processes of the ganglion 

 cells enter the medulla, pass dorso-medially through the formatio reticularis, and end in the 

 nucleus of termination in the floor of the fourth ventricle. The motor fibers arise from dorsal and 

 ventral efferent nuclei in the medulla. The glosso-pharyngeal shares these nuclei with the vagus 

 and has practically the same central connections as that nerve {q. v.). 



THE VAGUS NERVE 



^ The vagus (N. vagus) ^ is the longest and most widely distributed of the 

 cranial nerves; it is also remarkable for the connections which it forms with 

 adjacent nerves and with the sympathetic. It is attached to the lateral aspect of the 

 medulla by several filaments which are in series with those of the ninth nerve in 

 front and the eleventh nerve behind (Fig. 629). The bundles converge to form a 

 trunk which passes outward, pierces the dura mater, and emerges from the cranium 

 through the foramen lacerum posterius (Fig. 647). In the foramen the nerve bears 

 on its lateral aspect the elongated flattened jugular ganglion (G. jugulare). 



The ganglion communicates with — (a) the tympanic nerve, (6) The petrous ganglion of the 

 glosso-pharyngeal nerve, (c) the spinal accessory, and (d) the hypoglossal. It also gives off the 

 auricular branch (R. auricularis) , which runs forward below the petrous gangUon and passes through 

 a small canal in the petrous temporal bone to gain the facial canal. Here it gives filaments to the 

 facial and emerges with that nerve through the stylo-mastoid foramen. It ascends behind the 

 external acoustic meatus, dips under the deep auricular muscles, and passes through a foramen 

 in the conchal cartilage to ramify in the integument which lines the meatus and the adjacent 

 part of the ear. It may be noted that many fibers of the vagus pass over the medial face of the 

 gangUon without entering it. 



A ganglion nodosum in the form of a compact mass is not present in the horse. It appears 

 to be represented by masses of ganglion cells in the nerve trunk which begin in front of the origin 

 of the pharyngeal branch and continue a considerable distance behind the origin of the anterior 

 laryngeal nerve. 



Beyond the ganglion the vagus runs backward and downward with the spinal 

 accessory in a fold of the guttural pouch (Fig. 562). Then the two nerves separate, 

 allowing the hypoglossal to pass between them, and the vagus descends with the 

 internal carotid artery and crosses the medial face of the origin of the occipital 

 artery. Here it is joined by the cervical trunk of the sjonpathetic, and the two 

 nerves continue along the dorsal aspect of the common carotid artery in a common 

 sheath (Fig. 558).^ At the root of the neck the vagus separates from the sym- 

 pathetic, and from this point backward the relations of the right and left vagi differ 

 somewhat and must be described separately. 



-^ The right vagus nerve (Fig. 554) enters the thorax in the angle of divergence of 

 the right brachial artery and the truncus bicaroticus. It then passes backward and 

 slightly upward, crossing obliquely the lateral surface of the brachiocephalic artery 

 and the right face of the trachea. Reaching the dorsal surface of the latter near 

 the bifurcation, it divides into dorsal and ventral branches. 



1 Also commonly termed the pneumogastric nerve. 



2 There is formed thus a vago-sympathetic trunk. 



