238 Mammalia, 



ligamentous attacliment, a little anterior and inferior to the 

 Stylo-mastoid foramen whence issues the seventh nerve. 

 Removal of Part of the Cranial Wall in order to 



EXPOSE THE EoOT OF THE TRIFACIAL NeRVE. It will be 



well, before making the above dissection, to gently press away 

 from the cranial wall with the handle of the scalpel, the portion 

 of brain thereto adjoining, in order to see clearly the origin 

 of the cranial nerves in that part. In this way there will be 

 seen beneath the Cerebellum two stout nerve roots leaving 

 the Medulla, just opposite the external auditory meatus ; of 

 these, that directed forwards is the root of the Trifacial, and 

 that directed straight outwards is the Seventh nerve. Pos- 

 teriorly is seen a group of nerve fibres, mainly directed out- 

 wards; these constitute the group sometimes called the Eighth 

 Nerve*; but which really consists of three distinct nerves : the 

 Glosso-pharyngeal, Pneumo- gastric, and Spinal Accessory : 

 the two first of these being attached to the Medulla Oblongata 

 in the same line ; the last, the Spinal Accessory, taking its 

 origin chiefly from the spinal cord, and coming forward to 

 join the Pneumo- gastric in the foramen of exit, called the 

 jugular foramen. Lastly, anteriorly to the Trifacial will be 

 seen two fine nerves, one arising from the Yalve of Yieussens, 

 between the Cerebrum and Cerebellum, and extending for- 

 wards in the Dura Mater in the same direction as the main 

 bulk of the Trifacial, m%., the Fourth JN^erve (pathetic, or troch- 

 lear) ; the other, coming from the Cerebrum and directed 

 obliquely outwards, being the Third Nerve, or motor oculi. 



The Student will now take a saw, and make two incisions in 

 a general direction from the middle of the Brain to the root 

 of the Tongue. Of these the anterior should be taken just 

 behind the orbital ring, through the middle of the anterior 



* According to another arrangement, in wliicli the Cerebral nerves are 

 reckoned as twelve pairs, the Glosso-pharyngeal =: ix. ; the Pneumo-gastric =: 

 X. ; and the Spinal Accessory =r xi. 



