222 Mr. F. Nansen on the Histological Structure 



towards the dorsal surface *. In the funiculus dorsalis I have 

 been unable to discover any longitudinal fibres^ nor could 

 Alilborn do so in Petromyzon. This author, however, notes 

 the possibility that the granules observed by him in the 

 network may be divided fine longitudinal fibres ; but this 

 seems not very probable. I doubt the real existence of longi- 

 tudinal fibres in this part of the spinal cord, and regard the 

 nervous parts of the funiculus dorsalis as consisting exclu- 

 sively of what I have previously called the fibrillar xoeb^ 

 Golgi's " entrelacement nerveux diffus." This fibrillar web 

 is also found distributed in the other parts of the white sub- 

 stance among the longitudinal fibres in both the funiculus 

 lateralis and the funicidus ventral is ; it is, however, most 

 predominant in the more dorsal parts of the spinal cord, there- 

 fore, as stated, in the funicidus dorsalis and the funiculus 

 lateralis, especially in the dorsal parts of the latter. 



The Nerve-rods. — As already stated, I have often succeeded 

 in tracing the fibrilke passing to the ventral rods quite from 

 the grey substance, nay, even from their origin from ganglion- 

 cells ; but I have found this possible only exceptionally with 

 the dorsal nerve-rods. As regards a portion of the hbrillse 

 (those running most dorsally) at any rate I have been able to 

 trace them for a tolerably long distance from their entrance 

 into the dorsal nerve-rods ; but there has always been a small 

 space between them and the grey substance, in which they 

 could no longer be traced, while in this neighbourhood they 

 were also more diflused and divided up than towards the nerve- 

 rods. From this 1 conclude, as already mentioned, that these 

 nerve-fibres belong for the most part to the form which origi- 

 nates from the fibrillar web, while the fibrillse running to 

 the ventral nerve-rods principally originate from ganglion- 

 cells. As regards their size, the dorsal nerve-rods seem to be 

 considerably larger and to contain a good many more fibrillar 

 than the ventral nerve-rods, just as the field from which the 

 fibrillffi for the dorsal rods originate is considerably larger 

 than that from which the ventral fibrillae spring. 



* In transverse sections the longitudinal fibres always appear consider- 

 ably Avrinkled, so that a vacant space is formed around each of them, 

 which, as Ahlborn has also noted in I'etrovii/zon, indicates the original 

 form of the fibres. In transverse sections the divided longitudinal fibre 

 generally appears as a strongly-coloured mass upon the wall of this cavity. 

 "J he elliptical transverse section of this cavity I have been unable to 

 observe definitely as Ahlborn describes it ; it appt ars to me generally to 

 be nearly round ; tlicre are certainly many difierences, but these I regard 

 generally as artificially produced. 



