230 POISONOUS SERPENTS. 



must be accompanied with an increased secretion and great distension 

 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 apical outlet of the perforated fang.(l) 



The duct which conveys the poison, although 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 parietes of the 

 pulp-cavity or true internal canal of the tooth. This inflection com- 

 mences 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 longitudinal 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 described, to be perfo- 

 rated by the duct of the poison-fang. 



From the real nature of the poison canal it follows that the 

 transverse section of the tooth varies in form in different parts of the 

 tooth ; at the base it is oblong, with a large pulp-cavity of a corres- 

 ponding form, with an entering notch at the anterior surface ; farther 

 on, the transverse section presents the form of a horse-shoe, and the 

 pulp-cavity that of a crescent, the horns of which extend into the 

 sides of the deep cavity of the poison-fang, (PL 65, fig. 10) : a little 

 beyond this part the section of the tooth itself is crescentic, with the 

 horns obtuse and in contact, so as to circumscribe the poison-canal ; 

 and along the whole of the middle four-sixths of the tooth the section 

 shows the dentine of the fang inclosing the poison cavity, and having 

 its own centre or pulp-canal, in the form of a crescentic fissure, 



(1) The nasal salivary gland is shown at d, the labial gland at e : it is an enlargement of the 

 posterior part of this gland in the Serpents with large posterior grooved maxillary teeth that has 

 been mistaken (as in the Bucephalus) for a poison-gland. Besides the preceding glands the 

 lachrj'^mal glands placed behind the eye are often largely developed, and, by a direct course of 

 their duetto the palatal region of the mouth, contribute likewise their secretion to the lubricating 

 stream which is so much wanted and for so long a time iri the difficult and gradual process of 

 deglutition in the Serpent tribe. 



