284 THE NERVOUS SYSTEM 



meatus, parotid gland, integument of the temporal region 

 and of the ear and surrounding parts. It communicates with 

 the otic ganglion. The lingual branch is joined by the 

 chorda tympani, passes to the inner side of the ramus of the 

 jaw, crosses Wharton's duct, and is distributed to the pa- 

 pillae and mucous membrane of the tongue and mouth. It 

 communicates with the facial through the chorda tympani, 

 with the hypoglossal, and with the submaxillary ganglion. 

 The inferior dental branch passes between the internal lat- 

 eral ligament and ramus of the jaw to enter the inferior 

 dental foramen. Thence it traverses the dental canal in the 

 inferior maxilla to issue at the mental foramen. Here it di- 

 vides into incisor and mental branches ; the former con- 

 tinues in the bone to supply the incisor and canine teeth ; 

 the latter supplies the skin of the chin and lower lip. In its 

 course the inferior dental gives off the mylo-hyoid (before 

 entering the canal) to the mylo-hyoid and anterior belly of 

 the digastric, and dental branches to supply the molar and 

 bicuspid teeth. 



Four small ganglia, usually classed as part of the sympa- 

 thetic system, are connected with the three divisions of the 

 tri facial nerve. The ophthalmic, or lenticular, ganglion is 

 connected with the first division ; the spheno-palatine or 

 Meckel's with the second ; the otic and submaxillary with 

 the third. All these receive sensory fibers from the trifacial 

 and motor fibers from various sources. 



Functions. It is seen from the foregoing description that 

 the trifacial is the great sensory nerve of the head and face, 

 and the motor nerve of the muscles of mastication. The 

 small, or motor, division has properly been called the "nerve 

 of mastication." It is insensible upon stimulation before 

 it is joined by the third division of the sensory root. Its sec- 

 tion causes paralysis of the muscles of mastication on that 

 side. It cannot be doubted that the large root is exclusively 

 sensory at its origin, and the acuteness of that sensibility, as 

 c. g., in the teeth, is a matter of common observation. Im- 



