Roth, Spinal Accessory Neii'e. 483 



very fine calibered medullated fibers, their diameter varying 

 from 1.8// to 2.7// with a few reaching 3.6/7.. He found also 

 that the tenth nerve, i.e., the second thoracic, in which these 

 fibers first appeared, was the uppermost one which had a white 

 ramus communicans connected with it and furthermore he found 

 that this white ramus was composed ahnost entirely, so far as 

 its medullated fibers were concerned, of fibers of a similar cali- 

 bre to those first occurring in the anterior root of the tenth 

 nerve. The conclusion naturally followed that the fine calibered 

 fibers of the anterior roots were the white rami fibers and that 

 the first group of such fibers given off from an anterior spinal 

 root was that of the second thoracic. 



If these conclusions be correct, then it is clear that in the 

 dog there is a distinct gap between the first nerve which pos- 

 sesses a white ramus and the level at which the lowest root of 

 the spinal accessory nerve arises, this root being given off at 

 about the level of the seventh cervical nerve, three segments 

 above the level of the first white ramus. Such a condition does 

 not accord with Gaskell's view as to the significance of the 

 spinal accessory and it seemed that it might be of interest to 

 investigate the relations of the two structures, spinal accessory 

 and white rami, in other mammals with a view to ascertaining 

 whether the discord was of general occurrence or whether some 

 correlation really existed. 



For this purpose it seemed advisable to select first of all 

 some form in which the origin of the lowest root of the spinal 

 portion of the spinal accessory occurred at a decidedly different 

 level than in the dog. Bischoff (1832) in his comparative 

 study of the spinal accessory found that in mammals there was 

 a considerable difference in the distance to which the nerve 

 descended into the cervical region. Thus, he found that it 

 descended in the weasel to about the level of the second cervi- 

 cal nerve ; in the mole, rat and marmot to that of the third cer- 

 vical ; in the rabbit to that of the fifth cervical ; in the stone- 

 marten, stag, cat, wolf and man to that of the sixth cervical ; 

 and in the pig, dog, and calf to that of the seventh cervical. 

 Having regard to these data the rat was chosen as a suitable 



