136 



auditory nerve very earlv, and indeed almost arises sepa- 

 rately from the brain. It gives off a nerve above, which 

 is the 



5. R. acusticus ampullae posterioris (r. a. p.). — Is at 

 first opposed to the external surface of the glosso- 

 pharyngeus, and lies between it and the iitriculus, but 

 exchanges no fibres with it. It turns upwards, crosses the 

 glossopharyngeus just as the latter is bending downwards, 

 and becomes attached to the outer face of the lateralis, 

 but again does not mingle with it. Still coursing 

 upwards it crosses the lateralis, curves outwards over the 

 top of the posterior ampulla behind, and, now lying 

 externally to the ampulla, bends forwards to reach its 

 sense organ. 



The remainder of the posterior nerve is the 



6. R. acusticus lagenae (>'. /.). — Passes backwards 

 over the roof of the sacculus, gives off a bundle to that 

 part of its sense organ situated there, and then crosses 

 inwards and downwards to supply that part of the sense 

 organ situated on the inner wall of the sacculus near the roof. 



The Ramulus acusticus neglectus, with its sense 

 organ, is absent in the Plaice. In other fishes the Ramus 

 vestibularis, or anterior root^ramuli 1, 2 and 3, whilst 

 the Ramus cochlearis, or posterior root = 4, 5 and G + the 

 R. acust. neglectus. 



Nervus Glossopharyngeu s — -IX. 



Contrary to the condition found in Gadus and Me)iidia 

 the glossopharyngeus leaves the medulla by only one root. 

 This, however, consists of two large bundles, which, on 

 being traced into the brain are seen to belong to the 

 motor and communis systems. There are no cutaneous 

 fibres in the glossopharyngeus. In the two fishes above, 

 the motor fibres leave the brain by a separate root. 



