530 THE CRANIAL NERVES. 



membrane of the cheek, and the skin and mucous membrane of the lips ; 

 and 2d, the auricula-temporal branch (at), which turns backward and 

 upward behind the neck of the inferior maxilla, to be distributed to 

 the integument of the anterior wall of the external auditory meatus, 

 the anterior part of the external ear, and the adjacent temporal region. 

 From this branch a twig of considerable size is given off (/"), which 

 turns forward to join the facial nerve, and communicates to its branches 

 in front of this point a perceptible degree of sensibility. 



Continuing its course, the nerve enters the dental canal of the inferior 

 maxilla, through which it runs from behind forward, giving off filaments 

 to the teeth and gums of the lower jaw. It then emerges at the mental 

 foramen, and radiates, like the corresponding portion of the superior 

 maxillary division, in diverging branches and ramifications, which ter- 

 minate in the integument of the chin and edge of the under jaw, and in 

 the skin and mucous membrane of the lower lip. 



The remaining sensitive branch of this portion of the fifth is the 

 lingual nerve (/), which separates from it before its entrance into the 

 dental canal, sends filaments to the submaxillary gland, the sympathetic 

 submaxillary ganglion, and the adjacent mucous membrane of the 

 mouth, and is finally distributed to the mucous membrane and papillae 

 of the tip, edges, and surface of the anterior two-thirds of the tongue. 

 Finally, the motor branches are those (#, x, x} going to the temporal, 

 masseter, and two pterygoid muscles, and that which is distributed (y) 

 to the mylohyoid muscle and the anterior belly of the digastric. 



Physiological Properties of the Fifth Pair. The most prominent 

 and important character belonging to this nerve is that of its general 

 sen'sibility. The regions of the face to which it is distributed, namely, 

 the skin of the cheeks, the eyelids, the tip of the nose, the lips, mucous 

 surfaces of the anterior nares, and especially the tip of the tongue, possess 

 a tactile sensibility of much higher grade than most other regions of the 

 body. The nerve itself, with all its principal branches, is also acutely 

 sensitive to mechanical irritation, and will give rise to indications of 

 sensibility on being wounded or galvanized, under conditions when the 

 spinal nerves generally are nearly or quite inactive. 



But the most direct and conclusive experiment bearing on the physio- 

 logical functions of this nerve and its branches is that of dividing them, 

 either separately or together, by a transverse section. Either the infra- 

 orbital or mental nerve maybe divided, in the quadrupeds, at the points 

 where they emerge from the corresponding foramina in the maxillary 

 bones. A more decisive method is that of dividing the fifth nerve in the 

 interior of the cranium by a section passing through its trunk at the 

 situation of the Gasserian ganglion. This operation was first performed 

 by Magendie, and has since been frequently repeated by various ex- 

 perimenters. It may be done, upon the cat or the rabbit, by means of 

 a steel instrument with a slender shank and a narrow cutting blade 

 projecting at nearly a right angle from its extremity. The instrument 

 is introduced in a horizontal direction through the squamous portion 



