492 Journal of Comparative Neurology and Psychology. 



nervous system, while the spinal accessory fibers emerge from 

 the cord, but it must be remembered that in the one case the 

 fibers in question are afferent and in the other efferent in quali- 

 ty. In all its morphological and physiological characters, espe- 

 cially when studied from the comparative standpoint, the acces- 

 sory is closely related to the vagus, and the view, so strongly 

 supported by Fukbringer, that the accessory is really a portion 

 of the vagus, its nucleus being merely a downward extension of 

 the vagus nucleus, seems to represent the true significance of 

 the nerve. 



Whether or not the downward extension of the vagus nu- 

 cleus be dependent upon the development of the trapezius and 

 sterno-mastoid muscles, as the evidence presented by Furbkin- 

 GER seems to indicate, it is certain that comparative anatomy 

 shows us a gradually increasing size of the vagus nu- 

 cleus and its gradual extension into the spinal region. 

 What the cause which determines the direction of the 

 extension may be is at present unknown, but it is to be 

 noted that the motor vagus nucleus is a lateral nucleus and its 

 direct prolongation downward would therefore bring it into 

 most intimate relation with the cell column from which the spin- 

 al white rami fibers take their origin. In its continued down- 

 ward progress it may be supposed that it would gradually dis- 

 place the majority of the cells of the sympathetic column 

 throughout the spinal segments it traversed, forcing them to a 

 lower level, so that throughout the region occupied by the 

 extended nucleus, white rami fibers would be either wanting 

 or few in number, while below the termination of the nucleus 

 there would be a sudden increase in their number. This is 

 exactly the condition which the results recorded above seem to 

 show. 



There is one point, however, which such an explana- 

 tion fails to clear up, namely, the existence of a sec- 

 ond somewhat sudden increase in the number of white rami 

 fibers in connection with the first and second thoracic nerves. 

 The fact that this second outflow begins at about the level of 

 the lowest nerve participating in the formation of the brachial 



