THE HEAD AND NECK 



309 



mina. The tympanic bulla should be cleared and the tendons of 

 origin of tongue muscles removed from the jugular process. 



(a) The ninth (glossopharyngeal) nerve is farthest forward. 

 Its two main branches are the ramus lingualis to the pos- 

 terior part of the tongue, for taste, and the ramus pharyn- 

 geus, the latter entering the lateral wall of the pharynx. 



(b) The tenth (vagus) nerve bears an elongated ganglionic 

 enlargement, the plexus ganglioformis or ganglion nodosum. 



It lies immediately below the jugular for- 

 amen . The superior laryngeal nerve and 

 the ramus cardiacus (depressor nerve) 

 are given off at the level of the origin of 

 the internal carotid artery. Within the 

 jugular foramen of the skull, the vagus 

 bears a slight enlargement, usually double, 

 the jugular ganglion, and gives off a mi- 

 nute auricular branch which connects with 

 the ninth and seventh nerves and then 

 emerges from the petromastoid bone just 

 behind the external acoustic meatus to be 

 distributed in the external ear. 

 (c) The eleventh cranial, or spinal accessory 

 nerve (n. accessorius), is dorsal to the 

 vagus. The nerve passes dorsad to the 

 medial side of the mastoid attachments 

 of the sternomastoideus and cleidomas- 

 toideus muscles, giving branches to the 

 latter, and then passes backward to the 

 ventral surface of the trapezius to which 

 it is distributed. 

 (d) The twelfth (hypoglossal) nerve arises behind the foregoing 

 nerves, since it comes from the hypoglossal foramina of the 

 occipital. It crosses their roots, forming a broad curve on 

 the lateral surface of the root of the external carotid artery, 

 and enters the base of the tongue. The ramus descendens 

 is given off at about the point where it crosses the artery. 

 It has a slender root from the third cervical nerve. 



the 



extra-cranial roots of the 

 IX-XIl cranial nerves and 

 sympathetic trunk ; ven- 

 tral surface, right side, the 

 sympathetic and depressor 

 nerve shown as displaced 

 from the dorsal surface of 

 the artery. 9, 10, 11, 12, 

 glossopharyngeal, vagus, 

 spinal accessory, and hypo- 

 glossal nerves; ac, carotid 

 artery; c, cervical root of 

 ramus descendens XII; 

 gn, ganglion nodosum vagi ; 

 Is, superior laryngeal; nd, 

 ramus cardiacus vagi (de- 

 pressor nerve) ; rd, ramus 

 descendens hypoglossi ; s, 

 sympathetic. 



