REPTILIA. 



291 



fang of the large cobra (Jig. 34.), where a 

 fine hair is represented as passing through 

 the poison canal : in figure (a) the relative 

 position of the pulp cavity (x] to the poison 

 canal (y~) is shown in the plan of a longi- 

 tudinal section of a poison fang. 



The colubriform poisonous serpents of the 

 land have comparatively short venom-fangs, 

 but they are larger than those of the pelagic 

 serpents ; and behind the venom-fangs there 

 are likewise some smaller grooved teeth in 

 the maxillary bones : there are three such 

 teeth in the Bungarus pama, and five in the 

 Bungarus annulatus. In the Hamaclryas, or 

 great hooded poisonous tree-snake of India, 

 the venom-fang is relatively as large as in 

 typical poisonous serpents, but three or four 

 smaller grooved teeth are implanted behind 

 it on the maxillary bone. 



In the most deadly venom-snakes, as the 

 viper (Beriis\ the puff adder (Vipera), the 

 asps, or hooded snakes (Noja\\\\e rattlesnakes 

 (Crotalus) y the cophias and fer-de-lance (7H- 

 gonocephafusj, the poison fangs acquire their 

 largest size, and are associated only with 

 their successors : these are clustered in greater 

 or less number behind them, presenting the 

 same structure, but of a size proportionate 

 to their degree of development, and further 

 differing in being loosely imbedded in the 

 thick and wide mucous gum, which likewise 

 conceals the fixed and functional fang in its 

 ordinary position of retraction and repose. 

 This fang is more strongly curved backwards 

 than the ordinary teeth, but its acute and 

 slender apex is frequently bent slightly in the 

 contrary direction, as in the rattlesnake. 



The poison glands occupy the sides of the 

 posterior half of the head : each consists of 

 a number of elongated narrow lobes, extending 

 from the main duct which runs along the 

 lower border of the gland upwards, and 

 slightly backwards ; each lobe gives off lobules 

 throughout its extent, thus presenting a pin- 

 natifid structure; and each lobule is subdi- 

 vided into smaller secerning caeca, which 

 constitute the ultimate structure of the gland. 

 The whole gland is surrounded by a double 

 aponeurotic capsule (6), of which the outer- 

 most and strongest layer is in connexion with 

 the muscles (a), by whose contraction the 

 several ceeca and lobes of the gland are com- 

 pressed and emptied of their secretion. This 

 is then conveyed by the duct to the basal 

 aperture of the poison canal of the fang. We 

 may suppose, that as the analogous lachrymal 

 and salivary glands in other animals are most 

 active during particular emotions, so the rage 

 which stimulates the venom-snake to use its 

 deadly weapon must be accompanied with 

 an increased secretion and great distention 

 of the poison glands ; and as the action of the 

 compressing muscles is contemporaneous with 

 the blow by which the serpent inflicts its 

 wound, the poison is at the same moment 

 injected with force into the wound from the 

 apicial outlet of the perforated fang. 



The duct which conveys the poison, al- 

 though it runs through the centre of a great 



part of the tooth, is, nevertheless, as we have 

 seen, really on the outside of the tooth, the 

 canal in which it is lodged and protected being 

 formed by a longitudinal inflection of the pa- 

 rietes of the pulp cavity or true internal canal 

 of the tooth. This inflection commences a 

 little beyond the base of the tooth, where its 

 nature is readily appreciated, as the poison 

 duct there rests in a slight groove or longi- 

 tudinal indentation on the convex side of the 

 fang : as it proceeds, it sinks deeper into the 

 substance of the tooth, and the sides of the 

 groove meet and seem to coalesce, so that 

 the trace of the inflected fold ceases, in some 

 species, to be perceptible to the naked eye; 

 and the fang appears, as it is commonly de- 

 scribed, to be perforated by the duct of the 

 poison fang. 



The poison canal again assumes the form 



Fig. 211. 



Poison Apparatus of the Viper ( Vipera Berus, after 

 Brandt and Ratzburg}. 



a, the muscle inserted into the capsule of the 

 gland ; b, the aponeurotic capsule laid open ; c, the 

 poison gland laid bare ; d, capsule of the gum con- 

 taining the supplementary fangs ; e, a hair passed 

 into the poison duct, and into the poison canal of 

 the fang ; /, g, anterior supplementary fang. 



of a groove near the apex of the fang, and 

 terminates on the anterior surface in an 

 elongated fissure. 



Development of the Teeth. In the black 

 alligator of Guiana, the first fourteen teeth 

 in the lower jaw are implanted in distinct 

 sockets; the remaining posterior teeth are 

 lodged close together in a continuous groove, 

 in which the divisions for sockets are faintly 

 indicated by vertical ridges, as in the jaws of 

 the fossil Ichthyosaurus. 



The tooth germ is developed from the 

 membrane covering the angle between the 

 floor and the inner wall of the socket. It 

 becomes in this situation completely en- 

 veloped by its capsule, and an enamel organ 

 is formed at the inner surface of the capsule 

 before the young tooth penetrates the in- 

 terior of the pulp cavity of its predecessor. 



The matrix of the young growing tooth 

 affects, by its pressure, the inner wall of the 

 socket, and forms for itself a shallow recess : 

 at the same time it attacks the side of the 

 base of the contained tooth : then, gaining a 

 more extensive attachment by its basis and 

 increased size, it penetrates the large pulp 

 cavity of the previously formed tooth, either 

 by a circular or semi -circular perforation. 



u 2 



