630 TEXT-BOOK OF PHYSIOLOGY 



the fibers arborize around the nerve-cells composing it. Experiments 

 are lacking as to the function of the small petrosal. The small size of 

 its nerve-fibers and their termination would lead to the conjecture 

 that they are probably vaso-dilatator and secretor. Stimulation of Jacob- 

 son's nerve gives rise to a dilatation of the blood-vessels of, and secretion 

 from, the mucous membrane of the cheek, lips, and gums and of the 

 parotid and orbit glands, the regions of distribution of the post-ganglionic 

 fibers of the otic ganglion. This nerve therefore contains both vaso- 

 dilatator and secretor fibers (see pages 155, 634.). 



3. The tympanic nerve or stapedius nerve is distributed directly to the 



stapedius muscle, and as this muscle is of the striated or skeletal 

 variety it is innervated by the facial proper. 



4. The chorda tympani nerve is given off from the facial at a point about 



5 millimeters above the stylo-mastoid foramen. It then passes upward 

 and forward and enters the tympanum through the iter chords posterius, 

 crosses the tympanic membrane between the malleus and incus, leaves 

 the tympanum by the iter chordae anterius or canal of Huguier, and 

 finally joins the lingual branch of the fifth nerve. Some of its fibers can 

 be traced to the mucous membrane of the dorsum of the tongue, others 

 to the submaxillary and sublingual ganglia with which they become 

 associated. 



The^ determination of the origin, course, and functions of the chorda 

 tympani nerve has given rise to many investigations and discussions, and it 

 cannot be said that the results thus far attained are as satisfactory as might 

 be desired. 



If the chorda tympani nerve is divided there follows a contraction of 

 the blood-vessels in the neighborhood of and a diminution in the secretion 

 from the submaxillary and sublingual glands. Stimulation of the peripheral 

 end of the divided nerve gives rise to a dilatation of the blood-vessels and an 

 increased production and discharge of saliva from these glands (see page 

 153). From these results it is certain that the chorda tympani contains both 

 vaso-dilatator and secretor fibers. Nicotin applied to the submaxillary 

 and sublingual ganglia abolishes the effects of stimulation of the chorda 

 tympani. It does not prevent the same effects when the ganglia themselves 

 are stimulated. It is clear, therefore, that the vaso-dilatator and secretor 

 fibers arborize around the cells of the ganglia and are not distributed directly 

 to the gland structures. It is highly probable that the vaso-dilatator and 

 secretor fibers in the chorda tympani are the continuations of the efferent 

 fibers found in the pars intermedia and that they too have their origin in the 

 nucleus salivatorius. 



^ If the nerve be divided as it crosses the tympanic cavity or before it unites 

 with the lingual branch of the fifth nerve, there follows a loss of taste in the 

 anterior two-thirds of the tongue on the corresponding side, though the sensi- 

 bility remains unimpaired. For this and other reasons, the chorda tympani 

 has long been regarded as the nerve of taste for this region. The nerve-fibers 

 subserving the sense of taste are believed to be the peripherally coursing 

 fibers which have their origin in the nerve-cells of the geniculate ganglion 

 and which descending in the aqueduct of Fallopius are continued as the 

 chorda tympani. The nerve impulses developed in the peripheral termina- 

 tions of this nerve by the action of organic matter in solution are transmitted 



