OCR Text |
Show 1895.] TEETH OE CERTAIN POISONOUS SNAKES. 815 surrounding the grooved tooth, or becoming enlarged it communicates with the cavity surrounding the tooth by an aperture about equal in diameter to that of the duct. This opening is always towards the outer side of the grooved tooth (the first one when more than one is present), and may be situated either at the base of the tooth or a little way from it (PI. XLIV. fig. 15; PI. X L V . fig. 5). It will be seen from the above that the duct is not itself in direct communication with the groove of the tooth, but that the two communicate through the mediation of the cavity enclosed by the muscular folds surrounding the tooth, which are united in front. Consequently the loss of the tooth does not cause any injury to the duct, and in a short time one of the reserve teeth takes the place of the lost one. There are usually about half a dozen reservo teeth in successive stages of development behind the functional one, and they are in no way connected with the duct until called upon to replace a tooth that has been damaged or lost. The reserve teeth are posterior and internal to the functional ones, and are developed under cover of tbe expanded anterior extremity of tbe transpalatine bone ; their positions are indicated in fig. 11, PI. X L V. The grooved teeth are situated at the posterior extremity of the maxilla, and their number varies from one to three in different genera and species. They are generally much larger than the other maxillary teeth and also straighter, though, like them, they are directed backwards at a considerable angle. Some of the teeth are almost circular in section, others compressed, and all are more or less irregular. A few have distinct cutting-edges on the posterior face of the tooth, e. g. Leptodira rufescens (PI. X L V . fig. 12), Tham-nodynastes nattered (PI. X L V . fig. 16). The groove is situated as a rule on the antero-external face of the tooth, though in three observed cases it is directly external in position, viz.-Dryophis prasinus (PI. X L I V . fig. 12), D. mycterizans (PI. XLIV. fig. 13), and Oxybelisfulgida (PI. X L I V . fig. 21). In some the groove is almost closed, whereas in others it is widely open. It also varies in its extent down the tooth, for whereas in a few it almost reaches the extreme apex, in others, of which Dipsas irregularis is a notable example, it does not extend more than two-thirds of the way down. The mandibular teeth are as a rule about the same size and often more numerous than the maxillary, and they decrease in size in an antero-posterior direction; the most anterior teeth are more crowded and also placed in a more upright position than the maxillary teeth. The curvature is generally confined to the upper half of the tooth, and they are never recurved at the apex as is so often the case with the maxillary teeth. The Harderian gland in this group of Snakes is very variable in form and size, and may or may not be visible on removing the skin. In some it is a small elongated glandular mass, whereas in others it possesses two or three lobes and is of considerable bulk. A portion of it is always situated behind the eye, in the orbit. 52* |