1298 A MANUAL OF ANATOMY 



part of this foramen it joins the great deep petrosal nerve from the 

 carotid plexus to form the Vidian nerve, which passes forwards 

 through the Vidian canal into the spheno-maxillary fossa, and 

 joins the back part of Meckel's ganglion. The great superficial 

 petrosal nerve contains some motor fibres, but to a large extent it 

 consists of sensory fibres. These represent peripheral branches of 

 the unipolar cells of the geniculate ganghon, the central branches 

 of which give rise to the pars intermedia of Wrisberg. 



A communicating branch passes from the geniculate ganglion 

 to the small superficial petrosal nerve, which latter represents the 

 tympanic branch (Jacobson's nerve) of the glosso-pharyngeal, after 

 it has emerged from the tympanic plexus on the inner wall of the 

 tympanum. Through means of the small superficial petrosal 

 nerve this communicating branch is conducted to the otic ganglion. 



The external superficial petrosal nerve (sometimes absent) emerges 

 at a point just within the orifice of the hiatus Fallopii, and passes 

 to the sympathetic plexus around the middle meningeal artery. 



The nerve to the stapedius muscle arises from the facial nerve in 

 the descending part of the aqueduct of Fallopius, opposite the 

 pyramid of the tympanum. It enters a small canal in the p5n-amid, 

 and so reaches the stapedius as that muscle lies within the 

 canal. 



The chorda tympani nerve arises from the geniculate ganglion, 

 and it remains closely associated with the motor portion of the facial 

 nerve in the descending part of the aqueduct of Fallopius. A httle 

 above the stylo-mastoid foramen it leaves the motor portion of the 

 nerve, and passes upwards and forwards in a somewhat recurrent 

 manner through a minute canal, called the iter chordcB posterius, 

 by which it enters the tympanum. At first it is placed on the 

 posterior wall of the tympanum, close to the posterior margin of the 

 membrana tympani, and on a lower level than the pyramid. The 

 nerve then passes forwards upon the membrana tympani, near its 

 upper margin, lying between its mucous and fibrous layers, so as to 

 be ensheathed by the mucous membrane. In this part of its course 

 it passes over the inner aspect of the handle of the malleus. Having 

 arrived at the inner end of the fissure of Glaser, it leaves the 

 tympanum by passing through the iter chordce anterius or canal of 

 Huguier. It then enters the pterygo-maxillary region, and passes , 

 downwards and forwards imder cover of the external pterygoid I 

 muscle, where it receives a communicating twig from the otic i 

 ganglion, and thereafter joins the lingual nerve at an acute angle, 

 under cover of the external pterygoid muscle. The subsequent! 

 distribution of the nerve has been already described (see p. 1246).^ ! 



The chorda tympani is composed of fibres which are the peri-j 

 pheral processes of the unipolar cells of the geniculate ganglion ofj 

 the facial nerve. These represent the fibres which are distributed' 

 to the sides and dorsum of the tongue over its anterior two-j 

 thirds. They are, therefore, regarded as gustatory, or pertaining! 

 to taste, and functionally are afferent. They belong to the same 



