256 NERVE COMPONENTS OF BONY FISHES. 



Other forms such general cutaneous fibres may be present 

 in other cranial nerves, as in the ninth. 



We may now, perhaps, attempt to formulate a scheme 

 to express the typical branchiomeric nerve of higher fishes. 

 This nerve has a dorsal ramus to the skin, which contains 

 general cutaneous fibres and probably a few visceral fibres. 

 Motor somatic fibres are absent on account of the loss of 

 the dorsal musculature. The remainder of the typical 

 nerve is contained in the branchial trunk, which is com- 

 posed of visceral sensory and visceral motor fibres. From 

 this trunk is given off a palatine branch, which is all sen- 

 sory, and a pre-trematic branch, which is also sensory, and 

 a post-trematic branch which is mixed. 



Now, as the special sense organs are differentiated, 

 fibres from taste buds will come in by way of the palatine 

 and the pre- and post-trematic branches, and other com- 

 munis fibres from terminal buds on the outer surface 

 of the body may come in with the general cutaneous fibres 

 of the dorsal ramus. With the appearance of the lateral 

 line organs, their fibres may also enter with the dorsal rami, 

 though most of them appear to come in as independent 

 trunks. The latter may represent medial rami in which 

 the general cutaneous fibres have disappeared, or, more 

 likely, they have no representative in the spinal nerves. 



This scheme applies in the post-otic branchiomeres, 

 where the growth of the operculum has involved the 

 reduction of the ventral cutaneous areas. In the pre-otic 

 branchiomeres these relations are disturbed by the differ- 

 entiation of the jaws and of the facial skeleton in general, 

 and also by the exaggeration of the dorsal cutaneous 

 areas, since the whole operculum is morphologically a 

 dorsal or dorso-lateral structure belonging to the facial 

 segment. 



