4o8 Journal of Comparative Neurology. 



specialization and modification, in this case in connection 

 with the sense organs developed in the mouth and second- 

 arily in the outer skin. The acustico-lateral system is 

 evidently a later acquisition developed perhaps from the 

 general cutaneous system, perhaps from the terminal 

 buds. 



All of the components which I have enumerated were 

 therefore probably present in the typical primary branch- 

 iomeric nerve, except those for the specialized sense 

 organs, lateral line organs, taste buds, terminal buds, 

 and, of course, the organs of higher sense, eye, ear and 

 nose. The fibres for these specialized organs appeared 

 sporadically as evoked by the physiological requirements 

 of each case, and each, for obvious physiological reasons, 

 is related centrally to a single centre. In the case of the 

 cutaneous sense organs especially, these requirements 

 have been exceedingly variable. Thus the lateralis fibres 

 converge toward the tuberculum acusticum from either 

 side of the auditory capsule. The relations of the ganglia 

 and roots of these fibres are quite constant throughout the 

 fishes, as also are the principal nerve trunks, such as the 

 r. lateralis vagi, the r. ophthalmicus superficialis VII, the 

 r. buccalis and the r. mandibularis externus VII. But it 

 is quite different with the smaller lateralis branches, such 

 as the r. oticus, the r. supra-temporalis, etc. The courses 

 which these may take will depend partly upon the arrange- 

 ments of the corresponding organs and partly upon me- 

 chanical convenience growing out of the disposition of 

 adjacent organs, particularly other nerves, for it is a 

 general rule that two nerves which pass near each other, 

 whatever may be their composition, tend to fuse into a 

 common trunk. In the same way communis fibres from 

 terminal buds may accompany any of the cutaneous 



