IRISHES. 333 



trunk, over the pectorals, as well as others whicli go towards the 

 anal, where they form a longitudinal nerve like that of the back. 



This nerve is very large in the silures, and has been described in 

 the common silure, and in the lote by M. AA'^eber ; but it is found 

 much smaller, in many other fishes, and probably in all.* 



The seventh pair of nerves (y, .?), as in the other vertebrae belongs 

 to the gills, and arises on the sides of tlie medulla oblongata, between 

 the fiftli and the eighth pair, and is divided variously, to penetrate 

 into the sacs which contain the stones, and the ampullae of the semi- 

 circidar canals. It also contracts unions with the last branch of the 

 fifth pair (^). One of these vmions with the first branch of eighth or 

 gloss-pharyngeal (v, ii,) is constant. 



It is chiefly in the distribution of the eighth pair, that we may 

 admire tlie uniformity with which each nerve adheres in all classes, 

 to the performance of the same functions. 



The glosso-pharyngeal passes out of the cranium, sometimes by a 

 foramen of the lateral occipital, sometimes, as in the cod, by a foramen 

 of the jjetrous bone, and is distributed to the first branchia, to some of 

 the surrounding parts, and passes to the tongue, in which it is ex 

 panded. 



The vagus, jjroperly so called, comes ovit of the cranium through a 

 foramen of the lateral occipital larger than the preceeding, and some- 

 times dilates close to its origin, as in the carp ; at others, as in the 

 perch, this dilatation into a ganglion occurs at a greater distance ; the 

 ganglion (f) furnishes branches to the three last branchife, and to the 

 inferior pharyngeans. The trunk of the nerve is continued on the 

 pharynx, and follows the oesophagus to the stomacli. 



It will he observed that this distribution is the same, as that wliicli 

 obtains in the other vertebrat?e, with respect to the functions which the 

 nerve performs, the only ditfeience is, that it has modified its course 

 by going to the respiratory organ, because this organ itself has 

 clianged its place. 



But this pair furnishes another nerve, and sometimes two : whose 

 relation to those of the superior classes are not quite so apparent. 

 The first is a branch Avhich comes out sometimes from the anterior 

 base of this pair, sometimes from the posterior border of its ganglion, 

 passing in a straight line to the extremity of the tail. In a great 

 niunljer of fishes, particularly in the perch, after giving a superficial 

 twig (■^) which follows the commencement of the lateral line, this 

 nerve proceeds in a straight line (f) in the substance of the lateral 

 muscles, between the ribs and their appendices, receiving from all the 

 nerves of the spine, ditt'erent particidar twigs from the intercostals, and 

 furnishing twigs to the skin through all the intervals of the muscular 

 layers. 



In others, as in the cod, it is superficial throughout its entire 

 lengtli, and seems to have no commiuiication with the spinal nerves, 

 or if it has, at least, it is not easily traced. 



* We can have seen in the lote, the morue, the perch, the bar, the carp, the com- 

 mon sihire, the bagre, &c. That of the carp comes from the eighth pair, and not 

 from the fifth ; tliat of the silure on the contrary comes only from the fifth ; but in 

 the morue and perch, &c., it comes from both pairs. 



