206 OPHIDIA. — VIPERADiE. 



strated by Mr. Smith in the " Philosophical 

 Transactions " for 1818. This tube, although 

 completely enclosed, excepting at its basal and 

 apical orifices, must be considered as formed 

 merely by the closing round of a groove in the 

 external part of the tooth itself, and hence not in 

 any way connected with the inner cavity of the 

 tooth, in which exists the pulp upon which the 

 substance of the tooth is formed. The base of 

 the tooth, and consequently the basal orifice of 

 the tube just described, is embedded in a sac, 

 into which the poison is poured from the ducts of 

 the glandular structure by which it is secreted, 

 and which is believed to represent the parotid 

 gland of the higher Vertehrata. The poisonous 

 fluid itself is inodorous, tasteless, and of a yellow 

 colour. It is secreted in greater quantity, and 

 its qualities are more virulent in a high tem- 

 perature than in cold. Its secretion may be 

 greatly increased by local irritation ; as is evi- 

 denced by the following fact. Some years since 

 I was dissecting very carefully and minutely the 

 poison apparatus of a large Rattlesnake, which 

 had been dead for some hours ; the head had been 

 taken off immediately after death, yet as I con- 

 tinued my dissection the yellow poison continued 

 to be secreted so fast as to require to be occa- 

 sionally dried off with a bit of rag or sponge ; 

 I believe that there could not have been less 

 altogether than six or eight drops at the least. 



" Wlien the animal inflicts the wound, the 

 pressure on the tooth forces a small drop of the 

 poison through the tube ; it passes through the 

 external orifice, which is situated on the concave 

 side of the curved tooth, and is in the form of a 



