Stilling and Wallach suppose that these lines are continuous with the roots of the nerves; that they are, in fact, nerve-tubes proceeding from the grey matter to form these roots. But this supposition seems quite untenable, for the following reasons: 1st, because these lines are rnet with in situations intermediate to the points of emergence of the nerves ; 2dly, bemuse they pass to situations, such as the surface of the fissures, from which no nerve-roots einanate; 3dly, because, if they were nerve-tubes, they could not be so distinctly seen with so losv a power. It is rnuch more probable that they may be processes of grey matter prolonged to wards the surface, to which bloodvessels may pass from the pia mater, or simply bloodvessels passing from the pia mater to the g-rey matter. In some well-injected specimens, which Mr.Smee had the goodness to shew me lately, the blood vessels were seen to take exactly the same direction and course as these lines.
Besides the nerve-tubes which are found in considerable numbers in the grey matter, the branching processes of the caudate vesicles are met with in it also, which may be distinguished from the nerve-tubes by the absence of the white substance of Schwann, by their greyish colour, by their branching, and by their minutely granular texture. Capillary bloodvessels are met with in great numbers, ramifying in the grey matter, where they are much more nume rous than in the fibrous matter.
Stilling and Wallach describe a canal passing through the centre of the grey commissure, and extending, the whole length of the cord. This is certainly visible in most reg,ions, but not in all. It seems to me to have much more the appearance of a bloodvessel than of a canal. According to these authors, it is the persistent condition of the much-talked of canal of the spinal cord referred to at a previous page. Its situation in the grey matter seems rather op posed to this view. The point, however, is one upon which I am not prepared to express a decided opinion at present, and which de serves more extended careful examination.
From a review of the preceding statements, it is plain that a large number of fibres pass into the grey matter of the cord, and probably form some intimate connection with its minnt elements; and this fact is favourable to t supposition that the spinal nerves derive the origin, at least partly, from the grey matter. must be admitted, either that these fibres unit svith the vesicles of the grey matter in som way, or that they pass up to the brain throug the grey matter; the former seems the nio reasonable supposition, and more consiste with the apparent oblique or transverse dire tion which the fibres take in the grey matter.
The minute structiire of the medulla °Won gata resembles in many particulars that of th spinal cord. There is not, however, so com piete an isolation of the fibrous matter in it in the latter. Excepting in the anterior psra.
mids, and quite on the posterior and latera surfaces, the two kinds of nervous substance freely intermingle. The anterior and posterior pyramids and the restiform bodies consist, at least in great part, of longitudinal fibres, but the remainder of the fibrous rnatter appears to be inade up of transverse or oblique fibres. Most of these are doubtless connected with the roots of the many nerves which arise from the me dulla oblongata. Stilling refers to special ac cumulations of vesicular matter connected with the roots of each nerve, and which probably form its proper origin. These contain large vesicles. It is impossible to give an exact in terpretation to all the parts which are seen by his method of examination, imperfectly defined as they are from the use of such low mag nifying powers. It would be waste of time and space to do more than refer to the repre sentation given by Stilling ( fig. 397) of the structure, as viewed by a magnifying power of ten diameters. Nothing can be more true to nature, so far as it goes, but its correct explana tion must be sought for by diligent investigation with high powers. Numerous bloodvessels pe netrate the central matter of the medulla, and no doubt many of the lines, which Stilling supposes to represent fibres, -are in reality ves sels passing to the grey matter.
The mesocephale has very much the same kind of structure as the medulla oblongata; trans verse fibres (those of the pons) at its anterior part, longitudinal ones just behind these (pyra mids), with vesicular matter freely intermixed. Its posterior part is the same in structure as the optic thalamus, and consists of numerous fibres with an abundant quantity of grey matter. The inferior layer of the crus cerebri is purely fibrous; its superior portion is identical in structure with the optic thalamus, and the locus niger contains large caudate nerve-vesicles, with a considerable quantity of pigment con tained in them.
Microscopic investigation has as yet thrown no light on the direction and connections of the fibres of the cerebrum or cerebellum. What is known upon these points is derived from coarse dissection. The tubular fibres of which the white matter is composed, appear to be dis posed on different planes, and perhaps inter lace with each other, so as to render it difficult to isolate any plane to any great extent. This arrangement is more obvious in the cerebellum than in the cerebrum. The grey matter of both these segments contains the ordinary ele ments, caudate and spherical vesicles; but in the cerebellum those of the latter variety are much larger and more distinct than those which are met with in the brain. The peculiar struc ture of particular parts, as the optic thalami, corpom striata, tuber cinereum, &c. has been already described.