284 THE NERVOUS SYSTEM 



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 sympathetic 

 system, are connected with the three divisions of the trifacial 

 nerve. The ophthalmic, or lenticular, ganglion is connected 

 with the first division; the spheno-palatine or MeckePs 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 mastica- 

 tion." It is insensible upon stimulation before it is joined by the 

 third division of the sensory root. Its section 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, e. g., in the teeth, is a matter of 

 common observation. Immediate loss of sensibility in the area 

 of its distribution follows section, and even the cornea, which is 

 normally exquisitely sensitive, can be touched without exciting 

 pain. Both roots are usually cut at the same time, and besides 

 a loss of motion and general sensibility, section of this nerve 

 produces a decided effect upon the eye, the sense of taste, deglu- 

 tition and the nutrition of the parts to which the nerve is distrib- 

 uted. The flow of tears is increased, the pupil becomes tem- 

 porarily contracted and the ball protrudes. In a few hours 

 congestion is marked, and in a day or two the cornea sloughs and 

 the eye is destroyed. Section ot the fifth before its lingual 

 branch is joined by the chorda tympani from the facial causes 

 a loss of general sensation, but not of taste, in the anterior part of 

 the tongue; section of the lingual branch after it has received the 

 chorda is followed by loss of general sensation and of taste. This 



