THE TEETH OF REPTILES. 



249 



erect it would be much in the way ; when it is out of use, 

 however, it is laid flat along the roof of the mouth, and is 

 only erected for the purpose of striking j when in repose it 

 is altogether hidden by a fold of mucous membrane, which, 

 when it is erected, becomes tightly stretched over a part of 

 its anterior surface, and serves to direct the poison down 

 the poison canal by, to a great extent, preventing its escape 

 around the exterior of the tooth. 



The mechanism by which the poison fang is erected is 

 thus described by Professor Huxley (Anatomy of Verte- 



FIG. 105 (*). 



brated Animals, p. 241) : " When the mouth is shut the 

 axis of the quadrate bone is inclined downwards and back- 

 wards. The pterygoid, thrown back as far as it can go, 

 straightens the pterygo-palatine joint, and causes the axis 

 of the palatine and pterygoid bones to coincide. The trans- 

 verse, also carried back by the pterygoid, similarly pulls the 

 posterior part of the maxilla and causes its proper palatine 

 face, to which the great channeled poison fangs are attached, 



(!) Side and front view of the skuli of Craspedocephalus melas. A 

 bristle is passed down the poison canal. MX. Maxillary bones. Mn. 

 Mandible. PL Palatine bones. Pt. Pterygoid bones. Q,u. Quadrate 

 bone. T. Transverse bone. 



A. Side view. B. Front view. 



