ROOTS OF THE VAGUS GROUP. 9I 



greater difficulty. The ganglion of this component {jug. 

 g., the jugular ganglion of Shore and Strong, not of 

 Gaskell) is not sharply separate from the rest of the vagus 

 ganglionic complex, yet sufficiently so to make plain that 

 here, as in the tadpole (Strong, '95) it is the proximal 

 portion of the ganglion which performs this function. 

 Indeed we shall see below that the mode of origin of the 

 rami cutanei dorsales of the vagus would of itself be suffi- 

 cient to locate this ganglion quite precisely. 



The root fibres of this component are so intimately 

 intermingled with those of the large communis root, 

 which are of nearly the same size, that I found it impos- 

 sible to follow them into the brain in transverse sections. 

 In longitudinal sections they cannot be separately followed 

 all of the way from the ganglion to the terminal nucleus, 

 but at the superficial origin of the vagus the small bundle 

 of cutaneous fibres separates and, passing in between the 

 cephalic and caudal communis roots, turns abruptly caudad 

 into the spinal V tract. 



This root entering the spinal V from the vagus I have 

 found much larger in Haploidonotus than in Menidia and 

 Kingsbury ('97) reports it as well developed in Amiurus, 

 Perca, Roccus, Lepomis and Amia. Strong finds it also 

 in the tadpole and from Kingsbury's description ('95, p. 

 177) it is clear that the same relation holds for Necturus, 

 though Kingsbury was unwilling to admit the homology. 

 The occurrence of this root is probably general through- 

 out the Ichthyopsida. 



4. — The Motor Roots of the Vagus and Glossopharyngeus. 



i. — The Nucleus Ambiguus. — In the spinal cord I have 

 described in Section 3 two nuclei which are presumably 

 both motor, the nucleus of the ventral cornu and the para- 



