ROOTS OF THE VAGUS GROUP. 87 



communis, which runs along the lateral wall of the fourth 

 ventricle. Its fibres turn caudad and enter this fasciculus, 

 which in turn immediately enters the lobus vagi, as 

 already described. 



These fibres which enter the lobus vagi by way of the 

 fasciculus communis do not appear to differ in any way 

 from those which enter it directly from the vagus, for 

 their central and peripheral relations are essentially the 

 same. Indeed in those fishes which have larger lobi vagi 

 the IX nerve enters the lobus directly without participa- 

 ting in the formation of the fasciculus communis, as in 

 the cyprinoids (Mayser, '8i) and in the gadoids and Rani- 

 ceps (Stannius, '49). 



The IX ner^^e emerges close under the origin of the r. 

 lateralis vagi, its origin being covered by the ramus am- 

 pullae posterioris of the VIII nerve. These latter fibres 

 pursue an intracranial course as a thin flat band, running 

 up until they lie in contact with the r. lateralis vagi. The 

 IX root runs along the inner side of this acoustic root and 

 finally crosses it ventrally, the two roots lying as close to 

 each other as possible. There is certainly no extensive 

 anastomosis between these roots and probably there is no 

 exchange of fibres whatever, though from the nature of 

 the conditions it is impossible to be sure of the latter 

 point. 



It can, however, be clearly made out that a very small 

 bundle of communis fibres separates from the dorsal sur- 

 face of the IX root before this nerve has crossed the 

 VIII root. This bundle goes dorsad between the fibres 

 of the VIII nerve, already mentioned, and the medulla 

 oblongata and enters at once the lateralis root of the 

 vagus. Its further course will be described with that 

 nerve. 



