6 44 TEXT-BOOK OF PHYSIOLOGY 



comes associated with the spheno-palatine or Meckel's ganglion. In its 

 course it receives a filament known as the deep petrosal, from the car- 

 otid plexus of the sympathetic. The nerve-trunk formed by the union of 

 these two nerves is known as the Vidian nerve and terminates as 

 stated above. The character and function of the large petrosal 

 nerve have been a subject of much discussion. As the outcome of 

 modern methods of investigation it may be concluded that it is com- 

 posed mainly, if not entirely, of fine medullated nerve-fibers which 

 are the continuations of corresponding fibers in the nerve of Wrisberg 

 and that their destination is the spheno-palatine ganglion, around the 

 nerve-cells of which their terminal branches arborize. 

 Stimulation of the large petrosal, with induced electric currents, gives 

 rise to a dilatation of the blood-vessels of, and a secretion 

 from the mucous membrane, of the nose, soft palate, upper 

 part of the pharynx, 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 page 661). The nerve there- 

 fore 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 stimula- 

 tion of the spheno-palatine ganglion gives rise to the usual vaso-dila- 

 tator 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 pe- 

 trosal 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. From the 

 cells of the otic ganglion non-medullated nerve-fibers arise which 

 enter the auriculo-temporal branch of the trigeminal nerve and are 

 finally distributed to the blood-vessels and epithelium of the parotid 

 and other glands. 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 Jacobson'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, 662). 



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 



