OCR Text |
Show 1895.] TEETH OP CERTAIN POISONOUS SNAKES. 813 I always find them to conform to the tubulo-racemose type, and to consist of small polygonal lobules arranged round the branches of a duct. Moreover the nuclei are situated at the base of the cells and not in the middle, this being most markedly the case in the Proteroglypha, where the nuclei are more or less flattened against the bases of the cells. The Snakes treated of in this paper belong to the Colubridse, and all come under two of Boulenger's groups, viz.-the Opisthoglypha and the Proteroglypha. Of the latter only the Marine Snakes (the Hydrophiince) are here dealt with. Unfortunately many of the specimens were insufficiently preserved for histological purposes. They formed part of the teaching collection at the Eoyal College of Science, which Professor G. B. Howes kindly placed at m y disposal, together with specimens that he obtained for m e from the Natural History Museum and elsewhere. My very best thanks are also due to him for suggesting this investigation, and for many hints and much valuable information received during its progress, and to M r . G. A. Boulenger for kind assistance. COLLTBEID^. OPISTHOGLYPHA. Whether Opisthoglyphous Snakes should be regarded as truly poisonous or not is a matter over which there hangs considerable doubt. The gland in these Snakes which communicates with the posterior grooved teeth is functionally* very similar to that gland which is in communication with the fangs of the Proteroglyphous Snakes 2. In structure it is somewhat different, but I refer to it throughout this paper as the "poison-gland," as it is undoubtedly the homologue of that structure present in the Viperiue and Proteroglyphous forms. It is of a more or less oval form, always situated posterior to the eye, and as a rule a little below iu, its anterior extremity never reaching beyond the middle of that organ. The superior labial gland is an elongated band of glandular tissue extending along the whole of the upper jaw and skirting the lower edge of the poison-gland, encircling its lower half in such a manner that the two glands are often superficially indistinguishable, apparently forming one continuous structure (PI. XLIV. fig. 1 1 ; PI. X L V . fig. 10). Both glands exhibit a superficial lobulation, the lobules being polygonal in form and generally a little larger in the superior labial gland; there is often also a marked difference in colour between the two glands, the poison-gland being of a much lighter colour-generally a light yellow (in spirit-specimens), whilst the superior labial gland inclines 1 The bite of Dryophis and other Opisthoglyphous Snakes has been proved by several observers to be fatal to small animals. 2 The former is more or less embedded in the superior labial gland, whereas the latter is almost isolated from it, the superior labial gland here attaining its greatest bulk at the anterior extremity of the jaw. PROC. ZOOL. Soc-1895, No. LII. 52 |