456 UK. J. L. CLAEKE OX THE GEES srBSTAXXE OF THE SPLXAI, COED. 
canal for they may be found in different parts of the grey substance, and in the postenor 
iissure. The only difference between them and the nuclei found in the wMe columns 
and pia mater, is, that in the latter cases the granules or nucleoli are smaller^ but in t e 
Tortoise I have found that nuclei which, in every minute particular, resemo e 
those of the epithelium, may be traced continuously from the edge of the canal thioug i 
the whole of the grey substance and the white columns of the cord ■ . n ee , e spin 
caLl appears only J be the part where they are more thickly accumulated in l^and 
even there they are not enclosed in cells, but are connected only by a lanable n 
of fibres with the verge of the canal (see fig. 54, Plate XXII. G, and -planahon o 
Plate) There is good reason, then, for believing that both the epithehum and the small 
cells or nuclei by which it is surrounded, are allied to the connective tissue. 
The outer ends of the epithelial cells taper into delicate fibres of which those pro- 
ceeding from the columnar variety are the thickest (fig. 63, Plate XXII.). ese les 
radiate in all directions, and either run side by side, or cross each other in vaiaous ways 
and subdivide to join in an intricate network. For a considerable distance around the 
canal they may be frequently seen, as already stated, to be continuous with the small 
cells or nuclei above described. Some of them run directly backwards across the poste- 
rior commissure and along the posterior median fissure; some extend forwards across 
• the anterior commissure to the inner edges of the anterior columns, and may be traced 
in part to blood-vessels and pia mater contained in the median sulcus; while others run 
off in a lateral diiection and ai-e lost in the grey substance. In the filum termmle. 
where this substance, as already remarked, is reduced to a narrow fi-inge ( gs. _ c’ 
Plate XXIV.), their actual destination may often be very satisfactorily trace ) means 
of my method of preparation. Here they may be seen, sometimes at right angles, and 
sometimes more obliquely to the axis of the cord, to pass through the greg suhdance and 
then through the wMte colimins to join the connective tissue, every part ot ^^hlcix is 
interspersed with nuclei like those in continuity with the fibres in the central fringe. 
which here evidently consists of the same kind of tissue as the light-coloured space 
surrounding the canal in other regions of the cord. 
Hannovee regards the cells which line the cerebral ventricles as true nerve - celLs-^nd 
Biddee takes the same view of those round the spinal canal ; while Stilling considers 
them as epithelium, but, nevertheless, believes that the fibres uhich the) ghe o toim 
elementary parts of the primitive ?ierye-fibres and 7ierve-cells, with both of whic , 
according to him, they are directly continuous. He professes to have seen the peri- 
pheral ends of two epithelial-cells unite with each other after a shorter or longer course, 
and then enter a 7ierve-cell ; or the process of a nerve-ceW divides into two or three 
branches, which end in two or three epithelium-cells f. By the most careful examina- 
meiitous OP connectiye tissue, in opposition to Stilling, wlio considered it to 
and called it the circular commmure, but now calls it the “ substantia gektinosa centralis (see Philo.o 
phical Transactions, Part II. p. 614, 1851). 
* I have found the same in the Cat. . , , • , - iSwfrprev 
t “Zuweilen sieht Man die peripherischen Enden zweier Epithelialcylinder in kurzerer oder lancer . 
