THE HEAD AND NECK 1223 



base of the skull the glosso-pharyngeal, spinal accessory, and h>-po- 

 glossal nerves lie between the internal carotid artery and the internal 

 jugular vein. The glosso-pharyngeal nerv^e soon passes forwards 

 superficial to the artery, the spinal accessory nerve passes back- 

 wards superficial to the vein, and the hypoglossal nerve passes 

 forwards superficial to the artery at the lower border of the posterior 

 belly of the digastric muscle. 



Internal. — ^The ascending pharyngeal artery, the lateral wall of 

 the pharynx, the tonsil, and the superior laryngeal nerve. 



Development. — The internal caxotid artery is developed from the third 

 arterial arch and the part of the dorsal aorta above it. 



The Glosso-pharyngeal Nerve. 



The glosso-phar\Tigeal or ninth cranial nerve is a mixed nerve, 

 consisting of both afferent or sensory and efferent or motor fibres. 

 It emerges from the cranial cavity through the middle compartment 

 of the jugular foramen, along with the pneumogastric and spinal 

 accessory nerves, but enclosed in a separate sheath of the dura mater, 

 and lying on the outer side of, and anterior to, these two nerves. 

 In passing through the jugular foramen, the nerve presents two 

 ganglia, the upper one, which is small and situated in the upper 

 part of the foramen, being called the jugular ganglion ; and the 

 lower one, which is rather larger, being called the petrous ganglion. 

 The latter is about \ inch in length, and lies in the lower part of the 

 foramen, where it occupies a groove on the petrous portion of the 

 temporal bone. After emerging from the jugular foramen, the nerve 

 at first descends between the internal carotid artery and internal 

 jugular vein, being external to the line of the pneumogastric nerve. 

 It then passes downwards and forwards in front of the internal 

 carotid artery, and under cover of the styloid process, stylo- 

 pharyngeus muscle, and external carotid artery. It next cun^es 

 round the lower border of the stylo-pharyngeus, and crosses its 

 superficial surface in a forward direction. Finally, it passes beneath 

 the hyo-glossus muscle, and so reaches the posterior third of the 

 tongue, where it divides into its terminal branches. 



The jugular ganglion, as stated, is very small, and involves only a 

 few of the fibres of the nerve, the other fibres passing clear of, but 

 close to, the ganglion, and being continued into the nerve beyond 

 it. This ganglion neither gives nor receives any branches, and is 

 sometimes absent. 



The petrous ganglion, unlike the jugular, involves all the fibres of 

 the nerve, and it furnishes connecting branches and the t5mipanic 

 nerve. 



Branches of the Glosso-pharyngeal Nerve — i. From the Petrous 

 Ganglion — {a) Branches of Communication. — ^These are three in 

 number, as follows : one to the superior cervical ganglion of the 

 sympathetic ; one to the auricular branch of the ganglion of the 

 root of the pneumogastric ; and one to the ganglion of the root of 

 the pneumogastric. 



