484 Journal of Comparative Neurology and Psychology. 



form for study, especially as it was one readily obtained ; and a 

 study of the distribution of small medullated fibers in the anter- 

 ior roots of the cervical spinal nerves and in the rami communi- 

 cantes with reference to the lowest root of the spinal accessory 

 was made in that form. Some observations were also made 

 upon the cat and dog, but rats fully grown, formed the princi- 

 pal object of study. 



Before proceeding to consider the conditions in the rat it 

 is necessary to define what is meant by a white ramus fiber. 

 Gaskell limited the term to small fibers which were distinctly 

 grouped in bundles, and on this basis made a special point of 

 the occurrence of the uppermost white ramus communicans in 

 connection with the second thoracic nerve. But is such a lim- 

 itation justifiable ? Must it be supposed that fibers of the same 

 quality are always grouped together in distinct bundles ? Such 

 does not seem to be the case throughout the central system and 

 from what is known as to the association in bundles of fibers of 

 very different origin in both the central and peripheral systems 

 — e. g. the so-called mesial fillet fibers with the fillet in the 

 central system, and the chorda tympani with the lingualis fibers 

 in the peripheral system — it v/ould seem that the mode of 

 grouping of fibers so far as their quality or origin is concerned, 

 is, to some extent at least, fortuitous. It seems quite possible 

 that when but a relatively small number of white rami fibers 

 exist, they may not form a distinct bundle, but may be incor- 

 porated in a single trunk with grey rami fibers and may, if their 

 number be very small, be scattered among such fibers. In oth- 

 er words, it is possible that the ordinary use of the terms white 

 and grey ramus is merely relative, indicating merely the prepon- 

 derance in the nerve trunk of one or the other variety of fibers. 



The observations of Harman (1900) on the occurrence of 

 white rami fibers in man makes this possibility very prominent 

 and my observations upon the rami communicantes of the low- 

 er cervical and upper thoracic nerves of a dog are also of inter- 

 est in this connection. 



In sections of the ramus connected with the 6th cervical 

 nerve four distinct bundles were found. Three of these were 



