146 Journal of Comparative Neurology. 



It will be shown also that the peculiar appearance of the 

 nucleus dorsalis (Clarke's column) may suggest the partial 

 absence of another variable from the funiculi laterales. 



Microscopic Studies. 



Examination of a section taken from the intumescentia 

 cervicalis, even with the unaided eye, will reveal two prominent 

 features, one of which is peculiar. First, the fasciculus grac- 

 ilis is exceedingly well differentiated [F. g., Figs. 7 and 8). Its 

 relative depth is fully as great as in the human specimen at this 

 level. Further, at the periphery, it seemingly sends a lateral limb 

 over the outer periphery of the fasciculus cuneatus. A micro- 

 scopic examination shows that the axones composing the fasci- 

 culus gracilis are more closely bundled, and micro-measurements 

 prove that they have a smaller average caliber than those com- 

 posing the fasciculus cuneatus. If the fasciculus gracilis has 

 the meaning here it has in other mammals, its axones being 

 more compactly accumulated may perhaps be the result of the 

 fact that, arising from the ganglia spinalia of the inferior seg- 

 ments, they have run a longer course and become in conse- 

 quence more individually associated and more closely arranged 

 than those of the fasciculus cuneatus. 



Second, on examining a transverse section from the cervi- 

 cal segments especially, one's attention is immediately drawn 

 to an unusual feature. The two longitudinal fasciculi mentioned 

 above as occurring in the commissura grisea are both appreci- 

 able and well defined. They are placed, one on either side of 

 the mid-line, and tend to divide the commissura grisea into a 

 dorsal and a ventral lamina (A c. i.. Figs. 7 and 8). They 

 course more in the ventral portion of the commissura grisea, 

 however, for the canalis centralis is contained on their dorsal 

 side. Figure 9 is a detail from Figure 7, and is especially in- 

 tended to show this region of the section. Under the micro- 

 scope this dorsal portion of the commissure appears to be com- 

 posed largely of neuroglia (substantia gelatinosa centralis). No 

 nerve cell bodies are to be observed in it. However, it is trav- 

 ersed by quite a number of meduUated axones. These are con- 



