THE CRANIAL NERVES. 91 



of the skull, and immediately upon the mucous 

 membrane of the roof of the mouth. Near the 

 anterior end of the orbit it divides into two 

 branches, one of which runs outwards and 

 anastomoses with the ramus maxillaris of the 

 trigeminal nerve, while the other runs forwards 

 to the anterior part of the roof of the mouth. It 

 supplies the mucous membrane of the roof of 

 the mouth. 



Dissect this nerve from the ventral surface. Cut aivay the lower 

 jaw: carefully remove the mucous membrane of the roof of the 

 mouth, and find the nerve lying on the ventral surface of the eye- 

 hall and its muscles, and running parallel to and a short distance 

 from the skull-wall. Trace it backwards and forwards. 



ii. The ramus hyomandibularis runs outwards and 

 backwards round the front end of the auditory 

 capsule; it then crosses over the inner end of the 

 columella and turns downwards in the posterior 

 wall of the Eustachian tube to the angle of the 

 mouth, giving branches to the tympanic mem- 

 brane and to the articulation of the mandible. 

 It then divides into two branches. 



The exposure of the above nerve, which is 7iot easy, may he 

 performed thus : — remove the shoulder-girdle of one side ; also the 

 depressor manclidulce and temporalis muscles : open the cranial 

 cavity as before, to expose the braiyi : remove the tympanic 

 membrane and clean the outer end of the columella. Cut aivay 

 carefully the 7'oofof the auditory capsule by a horizontal cut, just 

 above the level of the columella : fiiid the facial nerve rinuiing 

 round the front end of the auditory capsule and in close contact 

 ivith it, and trace it hack over the columella and down to the angle 

 of the mouth. 



a. The ramus mandibularis runs forwards in the 

 floor of the mouth, lying along the inner edge 

 of the lower jaw and between the mylohyoid 

 nmscle and the skin, as far forward as the 

 chin. 



Dissect from the ventral surface : remove the skin from the 

 under surface of the floor of the mouth, and find the nerve running 

 along the inner border of the mandible. 



