392 OBIGINAL ARTICLES. 



of those round tlie spinal canal ; while Stilling considers them ad 

 epithelium, but nevertheless, believes that the fibres vrhich they give 

 off form elementary parts of the primitive nerve-Shrea and nerve-ceUs, 

 with both of which, according to him, they are directly continuous. 

 He professes to have seen the peripheral ends of two epithelial-cells 

 unite with each other after a shorter or longer coiu-se, and then 

 enter a nerve-ceU. ; or the process of a nerve-cell divides into two or 

 three branches, which end in two or three epithelium-cells. By 

 the most careful examination of some hundreds of preparations, I 

 have never been able to perceive that the epithelial processes are 

 connected with any other than the small cells or nuclei which I 

 have already described. I have sometimes seen the process of a 

 large nerve-ceU extend close up to the epithelium, but I have gene- 

 rally succeeded in tracing it round the canal to the opposite side of 

 the cord. If the processes of the epithelial cells were directly con- 

 tinuous with, and formed elementary parts of, nerve-ceUs and nerve- 

 fibres we might reasonably expect to find the number of the former 

 always in pro])ortion to that of the latter ; but the very reverse is 

 the case ; for, as we have just seen, in the Jilum terminale, where 

 both nerve-cell^ and ?^er^Je-fibres have entirely disappeared, the canal 

 is much larger, and the epithelial-cells are consequently much more 

 numerous than in any other region ; while, as I have already shown, 

 their processes may be traced through the surrovmding white sub- 

 stance as far as the surface of the cord." 



Dr. Eeissner describes the spinal cord of the Lamprey as being 

 colourless, and devoid of fibres having the characteristics of nerve- 

 fibres in other vertebrata. It presents neither anterior nor posterior 

 fissure, but simply a septum proceeding from the coimective tissue 

 around the central canal. The central canal itself is also divided 

 by the septum into two halves. The grey matter consists of fibres 

 and cells. The smallest cells belonging to the connective tissue. 

 Three kinds of larger cells are distinguished by M. Eeissner, viz. — 



a. Large inner cells — which are found towards the middle line of 

 the upper or posterior columns, have the form of flattened nuclei, 

 sending processes upwards and downwards, and some to the surface. 



/3. The large outer cells — have various forms, mostly elongated, 

 beginning at the external border of the grey matter — they send nu- 

 merous processes, as many as six from one cell — which form the axis 

 cylinder of the fibres going to the nerve roots, anterior commissure, 

 and longitudinal columns. 



y. ISmaller cells— tl\e9>e are scattered among the larger cells - then* 

 finer processes go to the posterior roots and to the radiating fibres of 

 the posterior commissure. 



Owsjannikow states that in fishes all the fibres of the spinal nerves 

 entering into the spinal marrow are connected with nerve cells. 



(Omnes cum cellulis gangliosis esse conjunctas) ; 



and that, in every coll, processes meet from the anterior root, from the 

 posterior root, and from the commissiu-es. That the white substance 



