ROOTS OF THE VAGUS GROUP. 97 



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, i. 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, z. 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 



