924 
ME. J. LOCKHAET CLAEKE ON THE DEVELOPMENT OE 
fissure it gave off a brush-like radiation of fibres that vrere continuous with those of the 
epithelium. In other sections, blood-vessels from the same process extended right and 
left, as well as backward and around the canal. Some of the fibres from the epithehal 
cells on each side of the front layer, after crossing the anterior commissure, penetrated 
the anterior white columns, at the sides of the fissure, and were lost in the tissue between 
its longitudinal fibres. Behind, a narrower portion of the epithelial layer was composed 
of the same kind of elements as those which were found in front ; and in a similar way 
fibres proceeding from their peripheral ends converged hackwm'd, to be continuous with 
blood-vessels and pia mater in the median fissure. Other fibres, also, from the 
same source could be traced into the posterior white columns. Around the remaining 
portion of the canal the epithelial layer was narrower and somewhat different in struc- 
ture. It consisted, for the most part, of round and of rather oval nuclei, irregularly dis- 
posed, and in connexion with the fibres on the outside of the layer. These nuclei, like 
the others just described, were finely granular, and in every way similar to a multitude 
of those which are scattered through the grey substance, and, as I shall presently show, 
through the tissue between the fibres of the white substance*. 
The large nerve-cells of the anterior cornu had assumed the shape and general appear- 
ance which they present in the adult cord. Like those of the cervix cornu posterioris, 
* This description of the epithelium in the human foetus has a general resemblance to that which I gave 
of the same structure in the full-grown ox (Phil. Trans. 1859, p. 455, Plate XXII. fig. 53) ; hut I have 
entered more particularly into details in the present case, on account of the close resemblance of the oval 
cells to the “ olfactory cells ” of the olfactory mucous membrane as first described by Schtjitze in the Prog 
and Pike. It is believed by Schultze and others, that the processes of these “ olfactory-cells” are directly 
continuous with fine fibres of the olfactory nerves. Such a connexion, however, has never, so far as I am 
aware, been actually seen. I have myself traced these nerve-fibres quite into the epithelial layer, but have 
not hitherto quite satisfied myself of their actual termination. Six years ago I showed that beneath tlie 
epithelium of the pharyngeal sac of the common earth-worm, a ganglionic plexus of nerves terminates in a 
network of single nucleated fibres, resembling in form a capillary network (Proc. Eoyal Soc. Jan. 1857, 
No. 24. vol. viii.). It is true that Axel Key (Archiv fur Anat. &c. 1861, p. 329) has described and figured 
in the tongue of the Prog, a remarkably conspicuous communication between nerve-fibres and cells which 
correspond to those of Schultze. But no such communication was observed either by Bilboth or Hotee 
(Archiv fUr Anat. &c. 1858 & 1859) in the same organ. On the fibres proceeding from the “olfactory cells” 
of ScHTJLTZE, there are slight granular dilatations, which I have found most remarkable in the Pike. On the 
fine fibres which surround the canal in the human foetus, as above described, and with which the processes 
of the oval epithelial cells are connected, I have also observed exceedingly minute dilatations. These fibres, 
as already stated, are evidently continuous, and identical in appearance with the fine fibres of the pia 
mater on the outside of the cord. Without, therefore, denying the possible continuity of the “ olfactory 
cells ” with true nerve-fibres, we must he so much the more cautious in admitting their actual continuity 
as an anatomical fact, until confirmed by actual observation. That the fibrous structure immediately 
surrounding the spinal canal is of the nature of connective tissue, was first maintained by myself (Plul. 
Trans. 1851) in opposition to Stilling, who described it (together with the epithelium, which he had not 
detected) as a “circular commissure” composed of grey nerve-fibres. In the human brain, also, the pro- 
cesses of the epithelium which extends from the aqueduct of Sylvius along the under surface of the poste- 
rior commissure, h ave clearly been seen by myself to pass through fissures in that commissure, to the pia 
mater on its opposite siuface (Proceedings of Eoyal Society for June . 20, 1861). 
