594 TEXT-BOOK OF PHYSIOLOGY. 



roof of the mouth, gums, and upper lip the regions of distribution 

 of the post-ganglionic fibers of cells of the spheno-palatine ganglion 

 (see Sympathetic). The nerve therefore contains both vaso-dilatator 

 and secretor fibers which belong to the autonomic system of nerves. 

 As after the administration of nicotine stimulation of this nerve is 

 without effect, and as stimulation of the spheno-palatine ganglion 

 gives rise to the usual vaso-dilatator and secretor effects it may be 

 inferred that the ganglion is the way station between the pre-ganglionic 

 fibers and the blood-vessels and glands. The deep petrosal, which 

 joins the large petrosal is in all probability a vaso-constrictor nerve 

 coming from the superior cervical ganglion of the sympathetic. There 

 is no evidence that the large petrosal contains any fibers from the 

 facial proper for the innervation of any striated muscle of the palate. 



2. The small superficial petrosal nerve is given off from the facial at a 



point somewhat external to the large petrosal nerve. In its course 

 it is joined by a small filament derived from Jacobson's branch of the 

 glosso-pharyngeal. Together they pass into the otic ganglion, where 

 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 check, 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 152, 598.) 



3. The stapedius nerve or tympanic 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 chordae 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 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 



