476 jacobson's nervous anastomosis. 



0/ Jacobson's Anastomosis,^ or the Nervous Plexus of the 

 Tt/mpanum and the Auricular Ganglion of Arnold. 



— The cavity of the tympanum receives nerves from various 

 sources, which communicate together upon the walls of that 

 cavity so as to form a plexus, and which are chiefly spent upon 

 the parts situated in the tympanic cavity. 



— This plexus is formed by branches from the great sympa- 

 thetic, the glosso-pharyngeal, the trigeminal or fifth pair, the 

 facial, the auricular ganglion, and the pneumogastric. 

 — This plexus, see fig. 205, is found on the outside of the walls 

 of the cranium, and on the outer face of the inner wall of the 

 cavity of the tympanum. It is observed in all animals endowed 

 with a tympanum : and in fishes that possess only an auditory 

 bulb, formed by the labyrinth, it is found spread in a few fila- 

 ments on the outer face of the bulb, the usual situation of the 

 tympanum in other animals. 



— Shortly after the glosso-pharyngeal nerve emerges from the 

 jugular fossa, it forms a gangliform enlargement, called the 

 ganglion of Andersch, from the anatomist who first described 

 it, or s^angUon petrosum, from its proximity to the petrous 

 bone. From this ganglion passes, upwards and forwards, the 

 nerve of Jacobson, and enters a small canal, the orifice of 

 which opens in the excavated border, which separates the 

 carotid canal from the jugular sinus. The nerve emerges 

 from the canal near the anterior border of the fenestra rotunda, 

 traverses the promontory, comes in front of the foramen ovale, 

 passes below the anterior part of the tensor tympani muscle, 

 and curves forward between this muscle and the Vidian nerve, 

 to terminate in the auricular ganglion of Arnold. 

 In the latter part -of its course it is parallel with the proper 



* The existence of this plexus was first made known by M. Jacohson, of 

 Copenhagen, who traced an anastomosing loop from the glosso-pharyngeal 

 nerve through the cavity of the tympanum, which there left branches, and 

 thence was reflected downwards to' join the third branch of the fifth pair. 

 Since then, the nerve has been shown to terminate, or arise in a ganglion, dis- 

 covered by Arnold of Zurich, on the lower surface of the third branch of the 

 fifth pair of nerves, called auricular ganglion, ganglion oticum, ganglion maxillo- 

 tympanique, — P. 



