218 Mr. F. Nansen on the Histological Structure 



by Ahlborn in Petromyzon. The fibrillte in this mass are 

 partly processes from the epithelial cells of the central canal, 

 partly processes from cells situated outside of these in the 

 grey substance (see further on) . On the dorsal side a thin 

 septum of fibrillar tissue extends from the central canal to the 

 pia mater. The fibrillte in this septum consist, at any rate 

 for the most part, of processes coming from the epithelial cells 

 of the canal and from circumjacent cells. By these two septa 

 or fibrillar masses the spinal cord is therefore divided into two 

 lateral symmetrical parts. 



The Grey Substance. — There is a considerable difference 

 between tlie grey and the white substance. The former, in 

 transverse section, has abroad and depressed form, correspon- 

 ding to the external form of the spinal cord. A distinction 

 of the anterior and posterior form is difficult to observe, and 

 its actual existence can only be made out by careful investi- 

 gation. In Fetromyzon Ahlborn was unable to demonstrate 

 the posterior horn. In Myxine I have found this possible, 

 having been able, by means of different methods of staining, to 

 trace the course of a great part of the fibrillfe which run to 

 the posterior nerve-rods directly from the vicinity of the grey 

 substance (see further on) ; it appears distinctly that the two 

 small " horns," which Ahlborn has also observed in Petro- 

 myzon^ and which are situated on each side close by the 

 above-named septum, which goes off dorsally from the central 

 canal, in reality correspond to a part of the posterior horn in 

 the higher Vertebrata, inasmuch as the greater part of the 

 fibrillas passing to the posterior rods can always be seen to 

 come from the white substance in the vicinity of these small 

 horns, or the portions of the grey substance lying nearest on 

 the outer side ; exceptionally I have been able to trace fibrilla3 

 quite from the small horns (probably originating directly from 

 cells here) and quite to the posterior rods. In the anterior 

 nerve-rods I have frequently been able to trace the fibrillar 

 quite from the ventral outer parts of the grey substance ; but 

 how much of the outer parts is to be referred to the anterior 

 horn I am still miable to ascertain. 



Just as in Petromyzon^ the ganglion-cells in the grey sub- 

 stance may be of extremely different sizes. There are some 

 which especially catch the eye by their remarkable magnitude ; 

 these are only few in number, and are regularly situated in 

 the outer, more lateral part of the grey substance, and there- 

 fore essentially in the part which must chiefly be referred to 

 the anterior horn. These cells, with their processes, generally 

 stain very strongly, especially with various aniline colours 

 (acid fuchsine, uigrosine, safranine, &c.). The smaller cells 



