THE CRANIAL NERVES. 593 



results of histologic investigation and physiologic experimentation would 

 indicate that it is composed of both afferent and efferent fibers. The afferent 

 fibers arise from nerve-cells composing in large part the ganglionic enlarge- 

 ment found on the genu of the facial nerve at the point where it turns back- 

 ward to enter the aqueduct of Fallopius. The cells of this geniculate 

 ganglion, originally bipolar present single axons which soon divide into 

 centrally and peripherally coursing branches. The centrally coursing 

 branches constitute in part the nerve of Wrisberg, which entering and pass- 

 ing through the pons terminates directly or indirectly around the sensor 

 end-nucleus of the glosso-pharyngeal nerve. The peripherally coursing 

 branches enter the sheath of the facial nerve and accompany it as far as a 

 point about 5 millimeters above the stylo-mastoid foramen. 



The efferent fibers which constitute in part the nerve of Wrisberg have their 

 origin in a group of cells situated beneath the floor of the fourth ventricle 

 near the median line between the 

 nucleus of the facial and the nucleus 

 of the motor root of the trigeminal 

 nerve and known as the nucleus sali- 

 vatorius. From its mode of origin, 

 the nerve of Wrisberg cannot be re- 

 garded as an integral part of the facial 

 nerve proper, but must be considered 

 as an independent nerve composed 

 of both afferent and efferent fibers. 



At the beginning and in the 

 course of the aqueduct of Fallopius 

 the facial trunk gives off the following 

 branches: the large superficial petro- 



sal, the small superficial petrosal, FIG. 278. CHORDA TYMPANI NERVE, i, 

 the Stapedius and the chorda tym- 3, 4- Facial nerve passing through the aqueductus 

 _ Q /- _Q\ Fallopii. 5. Ganglioform enlargement. 6. 



pam, (*ig. 278). Great petrosal n e rv e. 7. Sphenopalatine gan- 



I. The large superficial petrosal nerve glion. 8. Small petrosal nerve. 9. Chorda tym- 



is given off near the geniculate P a - I0 > I2 > *. Va - branches of the 



,. ... , r facial. 14, 14, 1 5. Glosso-pharyngeal nerve. 



ganglion. It then passes for- (Hirschfeld.} 

 ward into the spheno-maxillary 



fossa and becomes associated with the spheno-palatine or Meckel's gan- 

 glion. In its course it receives a filament known as the deep petrosal, 

 from the carotid 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 

 composed 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, 

 38 



