POISONOUS SERPENTS. 227 



tional elucidation by Mr. Smith's careful examinations of the fangs 

 of the Hydrus, Naja and Crotalus, and by Mr. CHft's illustrative 

 drawings appended to Mr. Smith's Paper(l). A true idea of the struc- 

 ture of a poison-fang will be formed by supposing the crown of a simple 

 tooth, as that of a Boa, to be pressed flat, and its edges to be then bent 

 towards each other, and soldered together so as to form a hollow cy- 

 linder open at both ends. The flattening of the fang and its inflection 

 around the poison-duct commences immediately above the base, and 

 the suture of the inflected margins runs along the anterior and convex 

 side of the recurved fang : the poison -canal is thus in front of the pulp- 

 cavity. The basal aperture of the poison-canal is oblique and its opposite 

 outlet is still more so, presenting the form of a narrow elliptical lon- 

 gitudinal fissure terminating at a short distance from the apex of the 

 fang. The relative position of the two apertures of the poison-canal 

 is shown in the figure of the fang of the large Cobra (PI. 65, fig. 9), 

 where a fine hair is represented as passing through the poison-canal : 

 in figure 1 1 , the relative position of the pulp cavity, a, to the poison- 

 canal, Z>j Z>, is shown in the plan of a longitudinal section of a poison- 

 fang. 



The character most commonly adduced from the dental system 

 as distinguishing the venomous from the non-venomous serpents is 

 that the former have two, the latter four rows of teeth in the upper 

 jaw : the two outer or maxillary rows being wanting in the venomous 

 species and their place being supplied by the single poison-fang. (2) 



canals or tubes do not communicate with each other, and are separated by a bony partition, 

 very brittle towards the basis, but which becomes somewhat stronger in proportion as it advances 

 towards the point. One of these tubes or canals, which I call the external one, because it is at 

 the side of the convex part of the tooth, begins, as has been seen, at the basis of the triangular 

 opening, and goes on enlarging by degrees to the middle of the length of the tooth, whence it 

 gradually narrows, and ends at the elliptical opening of the point. The inner canal on the con- 

 trary, which is towards the concave part of the tooth, begins with a large opening at the basis, 

 from whence it advances, closing by degrees, and terminates at length in a blind point above the 

 middle of the tooth. The partition Ukewise that separates the two cavities is crooked, and its 

 convex part is turned towards the hollow of the canal it terminates. The blind canal communi- 

 cates with the socket in which the tooth is fixed, and receives vessels and nerves." — Fontana, 

 On Poisons, Part I. Treatise on the Venom of the Viper, &c., translated by Skinner, 8vo. 

 2d Ed. 1795, p. 10. (The original Treatise was published in Italian, in 1765.) 



(1) Philos. Trans. 1818. 



(2) Compare figure 13, Naja, with fig. G, Python, in Plate 65 : the letter h shows the 



Q 2 



