XIII SNAKK-POISON 587 



badly poisonous snake has loieal sliields, i.e. a pair of shiekls 

 intercalated between the nasals and the preoeulars, but this 

 character is obviously no good for any practical purposes. There- 

 fore, unless you know a snake well enough when you see it, leave 

 it alone, because a mistake may be fatal. 



The poison is secreted in modified upper labial glands, or in a 

 pair of large glands which are the homologues of the parotid 

 salivary glands of other animals.^ A duct passes from the 

 gland forwards along the side of the upper jaw. Just in front 

 of the fang it doubles on itself, so as to open by a smriU pa]»illa 

 on the anterior wall of the sheath of mucous membrane which 

 embraces the base of the tooth like a pocket. As mentioned 

 before (p. 582), the poison is conveyed either along a furrow on 

 the anterior side of the tooth, or the growing substance of the 

 tooth partly converts the furrow into a canal which opens only 

 near the end of the tooth. This is a perfectly devilish contriv- 

 ance, ensuring the conveyance of th.e poison into the very 

 deepest part of the wound. The Elapinae have relatively short 

 fangs, while those of the Vipers, and especially those of the Crota- 

 line snakes, are much longer, sometimes measuring iiea^y an inch 

 in length. The most formidable apparatus is that of the Yiperidae, 

 since in them the maxillaries, each provided with only one 

 acting fang, and without any other teeth behind, can be erected. 

 The mechanism is explained in Fig. 154 and Fig. 179 (p. G47). 

 The apparatus of the upper jaw is so constructed that the 

 pushing forwards of the horizontal pterygoid bar will, by 

 acting on the ectopterygoid, rotate and erect the short maxillary. 

 The pulling forwards is effected by contraction of the spheno- 

 pterygoid muscle, which arises far forwards from the liasal 

 orbito-sphenoid region, and is inserted on to the inner dorsal 

 surface of the pterygoid. The principal closing muscles of the 

 mouth are the temporo- masseteric muscles (Fig. 179, T.a. and 

 T.p.) and the inner and outer pterygoid muscles, which latter 

 arise from the outer surface of the pterygoid bone, or from the 

 maxillary, and are inserted on to the articular region of the 

 mandilile. 



A strong ligament arises from the squamoso- quadrate 

 junction, and spreads fan -shaped upon the connective tissue 



^ For a detailed aiialoinioal account, see West, J. Linn. Soc. xxv. 1895, p. 

 419 ; xxvi. 1898, p. 517 ; and xxviii. 1900. 



