312 HEAD AND NECK 



There are still other points in connection with the glosso-pharyngeal 

 nerve which require mention. At the lower part of the jugular foramen 

 two small ganglia are formed upon its trunk, and from the lower of these 

 certain minute branches are given off. The upper ganglion is called the 

 ganglion superius ; the lower one is termed t\\e ganglion petroston. 



The superior ganglion is a small ganglionic swelling, which involves 

 only a portion of the fibres of the nerve trunk. It is placed in the 

 upper part of the bony groove in which the nerve lies as it proceeds through 

 the jugular foramen. No branches arise from it. 



The petrous ganglion is a larger swelling, which involves the entire 

 nerve-trunk, and lies at the opening of the jugular foramen, between the 

 vagus nerve and the inferior petrosal sinus (which intervenes between it 

 and the anterior border of the foramen). Its length is not more than two 

 or three lines. Three branches of communication enter or proceed from it. 

 These connect it with (i) the superior cervical sympathetic ganglion ; (2) 

 the auricular branch of the vagus ; and (3) the jugular ganglion of the 

 vagus. 



In addition to these twigs the tympanic nerve takes origin from the 

 petrous ganglion. 



Tympanic Nerve. The ultimate destination of this nerve may be 

 regarded as the otic ganglion, but it takes a very circuitous route to gain 

 that structure and it gives off branches on the way. It enters a small foramen 

 on the ridge which separates the jugular fossa from the carotid foramen 

 on the lower surface of the petrous bone, and it is conducted by a narrow 

 canal to the tympanic cavity. It crosses the inner wall of this chamber, 

 grooving the promontory. Having gained the anterior part of the 

 tympanum, it enters the bone a second time, and runs in a minute canal, 

 which tunnels the petrous bone below the upper end of the channel in 

 which is lodged the tensor tympani muscle. In this part of its course the 

 tympanic nerve is joined by a branch from the ganglion geniculi of the 

 facial nerve, and, after the junction is effected, it is termed the small super- 

 ficial petrosal nerve. 



The canal in which the small superficial petrosal nerve is lodged opens 

 into the cranial cavity upon the anterior surface of the petrous bone, 

 immediately lateral to the hiatus canalis facialis (O.T. Fallopii). Through 

 this the nerve emerges, and soon leaves the interior of the cranium by 

 passing downwards in the interval between the great wing of the sphenoid 

 and the petrous part of the temporal bone, or through the canaliculus 

 innominatus, or through the foramen ovale. Outside the skull it ends by 

 joining the otic ganglion. 



In the tympanic cavity the tympanic nerve gives branches of supply 

 (i) to the mucous membrane of the tympanum ; (2) to the lining 

 membrane of the mastoid cells ; and (3) to the mucous membrane of the 

 auditory tube (Eustachian). It is connected with the sympathetic plexus 

 on the internal carotid artery by the superior and 'inferior carotico-tympanic 

 branches which pierce the substance of the petrous part of the temporal 

 bone. 



Nervus Vagus. The vagus passes through the middle 

 compartment of the jugular foramen in company with the 

 accessory both being included within the same sheath of 

 dura mater. In the neck it pursues a vertical course, 

 lying, at first, between the internal jugular vein and the 

 internal carotid artery, and afterwards between the same 



