198 CLINICAL APPLIED ANATOMY. 



disease of the ophthalmic division is probably an irritative and 

 not a paralytic phenomenon, and so is not a result of anaesthesia 

 of the cornea, and consequent failure to remove irritating 

 particles. 



The areas of the face supplied by the three divisions of the 

 fifth nerve overlap each other ; the area supplied by the posterior 

 division of the second cervical nerve (the first has no posterior 

 division) also overlaps the posterior parts of the areas of the 

 first and second divisions of the fifth, while the skin overlying 

 the parotid gland is in part supplied by the great auricular 

 nerve, derived from the anterior division of the second cervical. 

 Consequently the areas of anesthesia produced by lesions of the 

 several divisions are much smaller than the anatomical distribu- 

 tion would lead us to expect. The boundary between the fifth 

 and cervical areas may be designated as the vertex-ear-jaw line, 

 since it extends from the vertex in front of the ear and along the 

 margin of the mandible. A line drawn through the supraorbital 

 notch to the interval between the two bicuspid teeth of the lower 

 jaw passes over the points of exit of the three divisions of the 

 fifth on the face. The infraorbital division appears close below 

 the lower margin of the orbit, and the mental nerve half way 

 between the alveolar edge and the lower margin of the jaw. 



The distribution of the fifth nerve to the mucous membranes 

 of the nose, mouth, and tongue, anterior parts of the palate and 

 fauces, and to the conjunctiva and cornea should be borne in 

 mind. The fifth nerve is not immediately concerned in the sense 

 of smell, but changes in the mucous membrane of the nose, con- 

 sequent upon lesions of the fifth nerve, may indirectly affect this 

 special sense. 



There is no doubt that taste fibres are present in the root, 

 and in the first, second, and third divisions of the fifth. It 

 is held that the taste fibres from the anterior part of the 

 tongue travel in the lingual trunk to the point where the 

 chorda tympani leaves it ; thence by the chorda tympani to the 

 facial trunk and geniculate ganglion, and from the latter by the 

 great superficial petrosal nerve to the sphenopalatine ganglion, 



