518 THE NERVOUS SYSTEM. 



these muscles. If it is divided on one side, the muscles on the 

 other side can still perform the act, but in an imperfect manner ; 

 if divided on both sides, all masticatory movements will be 

 abolished. 



Anastomosis of the Fifth Pair. Besides the branches already 

 mentioned, there are others which are termed anastomotic branches. 

 Although the upper, middle, and lower parts of the face are sup- 

 plied with sensation by the ophthalmic, superior maxillary, and 

 inferior maxillary divisions respectively, still the boundaries of 

 each are not absolute. Thus the skin of the nose is supplied by 

 fibers from the ophthalmic and superior maxillary, and the skin 

 of the temporal region is supplied from both the superior and 

 inferior maxillary divisions. In addition to these branches, there 

 are some which unite with other nerves and give a certain amount 

 of sensibility to the parts to which these nerves are distributed. 

 A striking instance of this is the branch which anastomoses with 

 the facial nerve. This nerve is at its origin purely motor, and is 

 distributed to the muscles of the face. These muscles are endowed 

 with sensibility ; but this is not due to fibers of the facial nerve, 

 but to those of the fifth nerve, which anastomose with the facial 

 and go with it to its termination in the muscles. 



Connection of the Fifth Pair with the Special Senses. After 

 division of the 'fifth nerve the special senses of smell, sight, taste, 

 and hearing are seriously affected. The Schneiderian membrane 

 becomes swollen, and later assumes a fungous condition and bleeds 

 readily when touched. There is besides an accumulation of altered 

 mucus in the nasal passages. The eye also undergoes marked 

 changes : The conjunctiva becomes congested and the cornea 

 opaque ; later, most of the structures of the eye suffer from inflam- 

 matory changes to the degree of destruction. The sense of taste 

 may likewise be lost, not only in the anterior two-thirds of the 

 tongue, but also in the posterior third as well. Besides, the sense 

 of hearing may also be greatly impaired. 



The explanation of these changes is not an easy one. Some 

 authorities regard them as due to disturbance of trophic in- 

 fluences. The nerve-fibers which form the posterior or sensory 

 root of the fifth pair in passing through the Gasserian ganglion 

 are reinforced by fibers which have their origin in this collection 

 of nerve-cells. Each of the three divisions of the trigeminus 

 contains, therefore, fibers of the posterior root, and in addition 

 fibers from the ganglion. The latter fibers are distributed to the 

 structures to which the accessory fibers are distributed, and they 

 are regarded as trophic nerves that is, as nerves which regulate 

 the nutrition of the parts to which they go. Among these parts 

 are the mucous membrane of the nose, the cornea, the conjunctiva, 

 and the tongue, and the loss of the special senses is believed to be 

 due to altered nutrition of the affected parts. The sense of sight 



