| OCR Text |
Show 1895.] TEETH OP CERTAIN POISONOUS SNAKES. 821 PROTEROGLYPHA. HYDROPHIIN^E. The poison-gland in Marine Snakes is situated some distance posterior to the eye. It varies somewhat in external form, and consists of a large series of longitudinally disposed tubules which converge anteriorly towards a central duct; this passes from the anterior end of the gland as the poison-duct. These tubules are larger towards the central axis of the gland and become smaller and much branched towards the periphery. They have spacious cavities, and their lining epithelium consists of short regular columnar cells. The cell-contents are for the most part aggregated at tbe base of the ceU, at which point the nucleus is situated; the rest of the cell presents a finely granular appearance. The poison-duct is of rather large calibre, and small tubules open into it along its whole course from the gland to the teeth, though they become much fewer in number anteriorly. As the duct nears the poison-fangs it becomes sinuous, bends suddenly inwards at the anterior extremity of the maxilla, and on reaching a point just anterior to the bases of the two grooved teeth it enlarges, enclosing a more or less considerable transverse vertical cavity. Into this cavity project two large cushions of muscular tissue, one in front of each tooth (PL X L V I . fig. 13 and 14, m). The two cushions are precisely similar and quite distinct from each other, the vertical slit between them being the only communicatiou between this cavity, enclosed by the enlarged termination of the poison-duct, and that enclosed by the folds which closely surround the teeth (PL X L V I . fig. 14). The muscular tracts extend a short distance parallel to the teeth down the inner edge of the fold. The fibres are arranged in such a manner that contraction would lessen the cavity at the termination of the duct, widen the passage between the two muscular cushions, and also bring the folds into closer approximation with the outer faces of the teeth. This ensures a free passage for the poisonous secretion from the duct to the bases of the grooved teeth. There is also a fold partitioning off the two grooved teeth from each other, and the secretion passes down one side to one tooth and down the other side to the other (cf. PL X L V I . fig. 14). As in the Opisthoglyphous Snakes, the reserve teeth are never in communication with the poison-duct until they become functional owing to loss of teeth previously in use. The labial glands are very similar to those previously described and have a series of ducts, which become very numerous at the anterior extremity of the jaw. Genus ENHYDRIS. Species examined:-E. hardwickii. The superior labial gland is of very small bulk posteriorly and much elongated, being but a thin line of glandular tissue under |
