92 THE NERVOUS SYSTEM OF THE FROG. 



/3. The ramus hyoideus is the posterior and larger 

 of the two branches : it runs forwards in the 

 floor of the mouth along the anterior cornu 

 of the hyoid, supplying its muscles. 



8. The auditory nerve, the nerve of hearing, arises from the 



side of the medulla immediately behind and in close 

 contact with the root of the facial nerve : it enters the 

 auditory capsule and ends in the internal ear. 



9. The glossopharyngeal nerve arises from the side of the 



medulla behind the auditory nerve, by a root common 

 to it and the tenth nerve : it leaves the skull by an 

 aperture immediately behind the auditory capsule, and 

 divides behind the capsule into two branches. 



i. The ramus anterior runs downwards and forwards 

 round the hinder border of the auditory capsule 

 and beneath the depressor mandibulse muscle to 

 join the facial nerve just after it has crossed over 

 the columella. 

 The dissection already made for the ramus hymondihularis of 

 the facial nerve will show also the above branch of the glosso- 

 pharyngeal. 



ii. The ramus posterior runs downwards and for- 



Avards to the ventral wall of the pharynx, passing 



beneath the fourth division of the petrohyoid 



muscle but superficial to the others ; it runs 



just behind and parallel to the anterior cornu of 



the hyoid. On reaching the floor of the mouth 



it crosses the hypoglossal nerve obliquely, lying 



dorsal to it, and then runs forwards in a 



peculiarly sinuous course, close to the middle 



line and between the geniohyoid and hyoglossus 



muscles, to the base of the tongue, which it enters 



and in which it ends. It supplies the petrohyoid 



muscle, and the mucous membrane of the pharynx 



and tongue. 



The exposure of the first part of the above nerve is best performed 



from the side, and is much facilitated by distending the oesophagus 



and pharynx with a cork or roll of pajjer. Its course along the 



floor of the mouth to the tongue should be dissected from the 



ventral surface. 



