132 



This it undoubtedly is in many Teleosts, but in tbe Plaice 

 it seems to correspond to palatinus and pre-trematicus ix. 

 fused together. Otherwise there is no pre-trematicus ix. 

 m the Plaice at all, or the whole of Jacobson's anastomosis 

 is that nerve, which is somewhat unlikely. 



The result, therefore, of the fusion of these two nerves 

 is a large bundle formed in greater part of communis ix., 

 but also to a lesser extent of communis vii. And as these 

 two components consist of exactly similar fibres, the final 

 course of each component can only be traced by degenera- 

 tion experiments. The combined nerve {com. vii. + ix.) 

 passes almost straight downwards on the inner side of the 

 large pseudobranch and divides into an anterior branch to 

 the mucosa of the roof and upper lateral wall of the 

 pharynx, and a posterior branch to the mucosa of the 

 ventro-lateral wall of the same. Although several of these 

 branches passed close, to the pseudobranch, none could be 

 traced into it, as Hei'rick also finds in Menidia. But the 

 nerve fibres are of very fine calibre and difficult to follow, 

 and as the pseudobranch has no other nerve supply it 

 must derive its innervation from this source, and indeed 

 dissection shows that it does do so. But whether its fibres 

 come from communis ix. or vii., or both, must be subse- 

 niuently determined. The large and well-developed 

 pseudobranch, however, may well explain the size of 

 .facobson's anastomosis. 



Near the origin of the post-trematicus some motor 

 branches are given off from the Truncus hyomandibularis 

 as in Menidia and Gadus. The truncus then passes out- 

 wards and downwards, and enters a canal in the hyoman- 

 dibular bone, as in Gadus. Soon afterwards it gives off 

 behind a lateral line nerve known as the : — 



8. Ramus opercularis superficialis vii. {op. s. vii.). — 

 This at once gives off two twigs which supply the last two 



