1224 A MANUAL OF ANATOMY 



(b) Branch of Distribution. — ^This is called the tympanic nerve, or 

 nerve of Jacobson. After leaving the petrous ganglion, it ascends, 

 in company with the tympanic branch of the ascending pharyngeal 

 artery, through the tjnnpanic canaliculus. In this way it enters 

 the tympanic cavity at the junction of the inner wall and floor, 

 and ascends upon the inner wall. Being joined by the carotico- 

 tympanic branch of the carotid plexus of the sympathetic, it 

 breaks up into branches which occupy grooves upon the promon- 

 tory, and form the tympanic plexus. From this plexus the tym- 

 panic nerve emerges under the name of the small superficial petrosal 

 nerve, which leaves the tympanic cavity and traverses a minute 

 canal in the petrous bone, passing in its course beneath the upper 

 portion of the canal which lodges the tensor tympani muscle. 

 Whilst in this canal, it is joined by a communicating branch from 

 the geniculate ganglion of the facial nerve. It emerges from the 

 canal through the accessory hiatus on the superior surface of the 

 petrous bone, which is external to the hiatus Fallopii, and then 

 passes forwards and inwards beneath the dura mater. Thereafter 

 it passes through the canaliculus innominatus, when present, or 

 through the fissure between the pars petrosa and great wing of the 

 sphenoid, or sometimes through the foramen ovale, into the zygo- 

 matic fossa, where it joins the otic ganglion, to which it conducts 

 glosso-pharyngeal and facial fibres. 



For a description of the tympanic plexus, see Index. 



2. From the Trunk of the Nerve. — (i) A communicating branch 

 sometimes passes from the nerve a little below the petrous 

 ganglion to join the digastric branch of the facial nerve. (2) A 

 carotid branch passes to the sympathetic plexus on the internal 

 carotid artery. (3) Pharyngeal Branches. — ^These are about four 

 in number. Three of them unite, over the middle constrictor of 

 the pharynx, with the subdivisions of the phar5mgeal branch of 

 the ganglion of the trunk of the pneumogastric, and with branches 

 of the superior cervical ganglion of the sympathetic, to form the 

 pharyngeal plexus. The other pharyngeal branch pierces the 

 superior constrictor, and is distributed to the mucous membrane 

 of the upper part of the pharynx. (4) A muscular branch to the 

 stylo-pharyngeus muscle, some of the fibres of which pierce the 

 muscle to supply the mucous membrane of the pharynx. (5) Ton- 

 sillar branches are given off near the tongue, which are distributed to 

 the tonsil and the anterior and posterior pillars of the fauces. 

 (6) Lingual or Glossal Branches. — Under cover of the hyo-glossus 

 muscle, the terminal part of the nerve divides into two branches, 

 dorsal and lateral. The dorsal branch passes to the dorsum of the 

 tongue, and is distributed to the circum vallate papillae and the 

 mucous membrane over the posterior third, extending as far back 

 as the front of the epiglottis. The lateral branch is distributed to 

 the mucous membrane of the side of the tongue over about its 

 posterior half. 



