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Show 1876.] MUCOUS MEMBRANE IN KANGAROOS. 173 of the one blends with that of the other. In this particular, as in most others, the lymphoid patches of the Marsupial stomach exactly resemble the patches of Peyer of the human ileum, only that in the latter the lymphoid follicles occupy more of the mucous membrane and come entirely to the surface, whereas, in the gastric patches in question, the follicles, as well as the remainder of the lymphoid tissue, are surmounted by tubular glands, except at the centre of each, where the surface is pitted in as far as the summit or cupola of the follicle. The glands over these lymphoid patches are somewhat shorter than those which are found in the rest of the mucous membrane of the second region, but entirely agree with them in structure (figs. 3 & 4). Transition of the Stratified Epithelium of the First Region into the simple Columnar Epithelium of the Second Region.-The manner in which this occurs will be readily understood by again referring to fig. 1. Close to the limit between these two regions the stratified epithelium (S) of the first is of considerable thickness, nearly as thick, indeed, as the whole mucous membrane of the second. If the lower line of the epithelium be followed, it will be seen that just as it approaches the junction it rises rather abruptly towards the surface, the layers of cells above it being continually less and less numerous until they are reduced to six or eight only. The lowermost columnar cells (c) of the stratified epithelium then become directly continued into the simple columnar epithelium (c) of the glandular region, whilst the layers above it cease abruptly, one or two cells often projecting at the edge like bricks from the end of a wall. The tubular glands begin immediately beyond this, the first ones passing down parallel with the ascending line of the stratified epithelium; but they are separated from it by somewhat more of the tissue of the mucosa than they are from one another. This tissue (i, i) contains very numerous lymphoid cells, and many are seen also in between the lower cells of the stratified epithelium of the immediate neighbourhood (at ly). Transitional forms of epithelium between the scaly stratified and the columnar (as described by Henle at the line of transition of gullet into stomach-epithelium in man) do not occur, but the passage of the one into the other is quite abrupt and effected by the cessation of all the layers of the stratified epithelium except the lowermost. Structure of the Second Region, in the neighbourhood of the Pylorus.-The lining membrane as well as the muscular coat is here very thick, especially in Macropus giganteus ; and the gland-tubes are correspondingly long (fig. 5). They are not enlarged at the fundus; and the cells of this are similar in appearance to those of the rest of the tube. Numerous bundles of muscular tissue (m!. m') pass from the muscularis mucosae upwards towards the glands. But the most striking feature of the part is the number and size of the lymphatics (I, I). These appear in sections as large well-defined clefts in the connective tissue between the glands. The clefts are not merely accidental; for they have a definite wall of flattened nucleated cells, like the commencing lymphatics elsewhere. |
