64 The Cranial Nerves 



tongue, to the mucous membrane of the neighbouring part of the 

 mouth, and to the sublingual gland. 



When the fifth nerve is paralysed (as also in the case of facial 

 paralysis, p. 68) the sense of taste on the tip of that side of the tongue 

 may be lost or impaired. 



Division of the gustatory (or lingual] nerve may be expedient 

 in the case of intractable neuralgia in the anterior part of the 

 tongue, as in lingual cancer. The nerve runs between the internal 

 pterygoid and the ramus of the jaw, and then lies just beneath the 

 mucous membrane of the mouth. Its exact position may readily be 

 made out in one's own mouth by passing the tip of the index-finger 

 downwards and backwards from the last molar tooth, and thrusting it 

 outwards into the hollow beneath the prominent alveolar ridge ; when 

 the nerve is thus pressed against the bone the sensation is unmistak- 

 able. To make sure of dividing the nerve, it is best to take out about 

 half an inch of it, which is easily done when the mouth is held wide 

 open by a gag and the tongue is pressed down ; the mucous mem- 

 brane having been raised from over the hollow below the alveolar 

 process, the nerve may be hooked up by an aneurysm-needle and de- 

 liberately dealt with. 



The inferior dental nerve descends between the lateral ligament 

 and the ramus of the jaw to the canal in the inferior maxilla. At its 

 origin it contains some motor filaments which it sends off to the mylo- 

 hyoid and the anterior belly of the digastric ; then, in the substance of 

 the maxilla, it supplies twigs to the teeth, and gives off the mental 

 branch, which emerges by the foramen under cover of the depressor 

 anguli oris. This branch is distributed to the mucous membrane and 

 s]f.m of the lower lip, and to the chin. 



The mental foramen is below the second bicuspid, in the vertical 

 line of the supra- and infra-orbital foramina. 



Irritation of filaments of the nerve in the pulp of some carious 

 tooth may give rise to disturbance in areas which are in anatomical 

 association : as, for instance, upon the front of the pinna, or in the ex- 

 ternal auditory meatus ; and thus it happens that the extraction of a 

 carious tooth may at once put an end to * ear-ache ' and ' face-ache.' 



The application of intense cold (produced by the ether-spray) in 

 the region of the external auditory meatus has such a numbing effect 

 upon the trunk of the nerve that under its influence a tooth may be 

 extracted from the lower jaw without the usual pain. 



Stretching or resection of part of the inferior dental nerve may be 

 needed in certain cases of inveterate neuralgia of the lower teeth. The 

 jaws being widely separated by a gag, a vertical incision is made 

 through the mucous membrane of the mouth, above and in front of 

 the insertion of the internal pterygoid (p. 8). Then, with a raspatory, 

 the mucous membrane is freely raised, and the nerve is found entering 

 the dental foramen. Unless the nerve be separated from the acconv 



