Herrick, Nerve Components of Bony Fishes. 253 



glionic) fibres go out with all of the roots from the com- 

 munis system and that these fibres are so similar to the 

 corresponding fibres which go out with the first spinal 

 roots that they are capable of functional substitution for 

 them. 



In a preceding section we suggested the theory that in 

 the oblongata the unspecialized visceral sensory centre 

 corresponding to that of the spinal cord has had differen- 

 tiated from it the special sensory system for the terminal 

 buds, a sensory system which is not represented in the 

 spinal cord. So also in the head there seems to have been 

 a special differentiation of the viscero-motor system (nu- 

 cleus ambiguus, motor VII and motor V) co-ordinate 

 with the development of the branchial motor apparatus, 

 which we know to be derived, not from the somites, but 

 from the splanchnic musculature. 



The suggestion made by Cole in a recent paper ('98, p. 

 233, foot note) is interesting in this connection: "A pos- 

 sible explanation of the vagus, I think, is that the bran- 

 chial nerves are secondarily sympathetic, /. e. , in function 

 only, whilst the visceral nerve is primarily sympathetic, 

 i. e., represents a modified portion of the sympathetic, and 

 thus both physiologically and morphologically belongs to 

 that system. Its connection with the vagus is thus a 

 ' blind ' and of precisely the same significance as the con- 

 nection of the sympathetic with the trigeminus and 

 facialis." The viscero-motor fibres of the trunk belong 

 to Langley's type of pre -ganglionic fibres, /. e., they ter- 

 minate in sympathetic ganglia and reach their appropriate 

 visceral muscles only through the mediation of sympa- 

 thetic fibres. The same may hold true of the viscero- 

 motor fibres of small calibre which go out with the vagus, 

 but it is certainly not true of the motor fibres of large size 



