Researches on the development of the spinal cord in man, mammalia, and birds / by J. Lockhart Clarke.

  • Clarke, J. Lockhart (Jacob Lockhart), 1817-1880.
Date:
1863
Catalogue details

Licence: Public Domain Mark

Credit: Researches on the development of the spinal cord in man, mammalia, and birds / by J. Lockhart Clarke. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    and has gradually blended with the anterior grey substance; while its inner border forms the epithelial layer (s) surrounding the central canal. Along the sides of the canal, the epithelium, as regards its constituent elements, differs but little in appear- ance from the rest of the grey substance. The only apparent differences are, that its nuclei are less closely aggregated; that the fibres radiating through their interspaces from the verge of the canal, and which are thicker, are consequently seen to be more continuous and branched; and that a few of its nuclei are larger, while others are more elongated or fusiform at right angles to the axis of the canal. Nor is it bounded externally by any definite line, but is continuous, as a nucleated network, with that of the anterior cornu. From the posterior margin of the elliptical canal its radiating fibres extend outward and backward into the posterior cornua, and directly backward between them into the posterior median fissure. In front of the canal, however, the epithe- lium has a somewhat different arrangement. At this part it forms a deeper and more distinct layer, containing more of the fusiform nuclei, which are elongated in a direc- tion forward, and terminate at each extremity in a fibre. At the sides of this layer the nuclei with their fibres are curved inward, but become progressively straighter as they approach the middle line (see figs. 4 & 8). Posteriorly their processes or fibres are thicker, and attached by their extremities to the margin of the canal; while anteriorly they converge across the anterior commissure, as a conical network, into the anterior median fissure, where they become directly continuous Avith the fibres of the pia mater and connective tissue enveloping numerous blood-vessels and derived from the circum- ference of the cord (m, figs. 4 & 8). In many cases the epithelium in front of the canal differs but little in appearance from the rest' of the layer, except that the principal fibres of the network converge forward to join the process of pia mater in the anterior median fissure. In such cases it has a general resemblance to that seen in fig. 9, Plate XLV., which exactly represents a portion of the canal and surrounding grey substance of a human foetus of nine weeks, magnified 420 diameters. It was taken from the same foetus as the section represented in fig. 8, Plate XLVI. o is the anterior part of the canal; s, s, between the canal and the outer line, is the layer of epithelium, which on each side, however, is seen to be gradually continuous with the anterior grey substance, f; while in front it terminates in a conical, network of connective tissue interspersed with nuclei, and continuous (at m) with the pia mater of the surface. I have next to show that the elements of the grey substance, which in fig. 3 were nearly uniformly alike, have in fig. 4 become more or less modified both in structure and arrangement. In fig. 3 every nucleus had a plain or smooth appearance, without any trace of granular contents or of a distinct enveloping membrane. In fig. 4, however, both these modifications of structure had taken place; and although the observation of this fine distinction might seem to be trivial and unimportant, it will nevertheless be seen, as we proceed, to be well worthy of attention. It was also observed that in section 3 the nuclei were very nearly of the same size in all parts of the grey sub- stance. In section 4, however, those of the anterior grey substance had everywhere