CRANIAL NERVES. 333 



ship exists between this nerve and the muscles and nerves of degluti- 

 tion. 



A remarkable fact in connection with the trigeminus is its great 

 functional resistance to various poisons which are capable of paralyz- 

 ing nerves of sensation. While all other regions of the body show 

 the effects of anaesthetics, those under the dominion of the trigem- 

 inus still preserve a high degree of sensibility. Even though a 

 patient be anaesthetized with chloroform, yet will he perceive punc- 

 tures in the temples and frontal regions. This occurs in spite of 

 the fact that sensations are not perceived elsewhere. 



Motor Functions. By its short root the trigeminus holds under 

 its power the movements of elevation, depression, and rotation of 

 the lower jaw. If this root be cut, it is found that the muscles con- 

 cerned in the performance of the above-mentioned movements are 

 paralyzed. The lower jaw remains passively separated from the 

 upper. 



Trophic Function. Within twenty-four hours after intracranial 

 section of the trigeminus, the cornea becomes opaque. At the end 

 of five or six days the cornea becomes very white in color. The iris 

 becomes inflamed and covered with false membranes. In about eight 

 days the cornea becomes detached and the contents of the eye escape. 



The suppression of the fifth pair is followed by remarkable 

 alterations in the Schneiderian membrane. It becomes spongy, and 

 bleeds upon the least touch. The place where the olfactory bulbs 

 lie is completely changed. Thus the acts of olfaction and vision are 

 indirectly affected. 



. Pathology. By reason of the intimate association of the trigem- 

 inus, and its Gasserian ganglion, with the petrous portion of the 

 temporal bone, it is exposed to all of the shocks and blows that are 

 able to fracture this bone. 



The relations of the trigeminus with its meninges are very apt 

 to be disturbed seriously by the presence of tumors. The false mem- 

 branes which are found in meningitis compress it and so produce 

 atrophy. The exudates of tubercular meningitis very often produce 

 anaesthesia of the face. 



The fifth pair is mo^t often the seat of either excessive sensi- 

 bility or paralysis. It is, perhaps, the one nerve which is the most 

 frequently affected in neuralgia. The relative nearness of the tri- 

 geminus to its sensory center probably explains the acuteness of the 

 pains in neuralgia. 



