SPINAL NERVES OF THE WHITE RAT. 14! 



The group just mentioned has been thus far found only in the 

 dorsal roots of young white rats having a body- weight of 4, 5, 6 

 and 7.5 grams respectively, and in an adult gray rat; suitable 

 preparations from the spinal cord of the adult white rat not being 

 at the moment available. 



The exact location of the new group of cells differs at different 

 levels of the spinal cord. The above statements on the general 

 character of the cells found, as well as the following description, 

 is based on a study of the young white rats alone. 



Semidiagrammatic illustration of the cross section of the spinal cord of the white 

 rat: I, lumbar cord; 2, thoracic cord; 3, cervical cord. = posterior root; 

 b = anterior root ; c = spinal ganglion ; d = new group of the cells. 



In the lumbar region, these cells lie in the dorsal root fibers 

 rather near the spinal ganglion, where the root enlarges slightly 

 and forms an extension ventrally (Fig. i). This local enlarge- 

 ment, however, is due to the fact that at this point the dorsal 

 root fibers take a somewhat wedge-shaped course and the nerve 

 cells lie around the pointed tip of the wedge. The total number 

 of the cells seems to vary according to the individual. A single 

 section, 6 micra thick, contains usually one or two cells, though 

 sometimes more can be seen. Since the preparations employed 

 were not made for the purpose of the present investigation and 

 did not form a complete series, the writer was unable to deter- 

 mine the total number of the cells contained in one nerve root. 

 In one case 26 cells were counted in twenty-three successive 

 sections through a single root. 



In the thoracic region the cells are located in an enlarged 

 portion of the dorsal root as in the lumbar region (Fig. 2). The 

 total number of the cells in the thoracic root seems greater than 

 in the lumbar root. 



In the cervical region this cell group is slightly modified. The 

 cell-bodies lie within the dorsal root where it exhibits a slight 



