132 



AYERS. [Vol. VI. 



In Petromyzon the rami anterior and posterior of tlie auditory- 

 nerve pass directly from the auditory foramen to the ampullae, 

 and as they approach the ampullar walls, they both divide into 

 two branches each, which end in the cristas acusticae of the 

 ampullas. 



The posterior ramus gives off a branch near the place where 

 it separates from the anterior ramus, and this branch supplies 

 the lagenar organ. The ramus anterior sends many fibres to the 

 utricular sense organ and to the organ in the recessus utriculi. 



The so-called ramus accessorius acustici accompanies the 

 VIII through the auditory foramen and is closely bound up 

 with it. According to Johannes Miiller, the accessory branch 

 is a part of the VII nerve, and from its distribution the facial 

 nerve, as I find, supplies directly and independently two of 

 the auditory sense organs and possibly also the ciliated epi- 

 thelium, though there is no sufficient reason for doubting that 

 the auditory proper may supply the ciliate epithelium in the 

 parts of the ear to which it is distributed. It must not be for- 

 gotten, however, that the innervation of the ciliate epithelium 

 has never been determined. It is usually stated that this 

 unique lining of the Lamprey's auditory organ is innervated by 

 the accessory nerve, and while I think this highly probable for 

 the part of the ear within reach of this nerve, I believe the two 

 branches of the auditory take part in the control of ciliate epi- 

 thelium. This would call for motor fibres in the auditory nerve 

 of Petromyzon, — not equivalent to musculo-motor nerves, per- 

 haps, but none the less motor. 



Ahlborn (1883, i), p. 269, says of the auditory roots inside 

 of the brain : " Alle die Elemente, welche in der beschriebenen 

 Weise mit einander den Gehornerven konstituiren, gelangen 

 nun theils durch die obere theils durch die untere Wurzel aus 

 dem Hirn, wie es in den einzelnen Fallen angegeben ist ; den- 

 noch ist die Trennung der beiden Wurzeln im Innern des 

 Gehirns keine principielle, und gerade so wie die beiden Ner- 

 venkerne in einander iibergehen, so treten auch einzelne Fas- 

 erstrange des unteren Kernes mit der oberen Wurzel aus dem 

 Hirn, und umgekehrt solche des oberen Kernes mit der unteren 

 Wurzel. Beide Wurzeln vereinigen sich wieder in Ganglion 

 Nervi acustici, durch dessen Vermittlung sie endlich in das 

 Gehororgan eing-efuhrt werden." 



