THE OPHIDIA. 241 



and lies on the outer side of tlie posterior nasal aperture. 

 Its anterior end is connected only by fibrous tissue with the 

 base of the skull. The inferior edge of the palatine bears 

 a few small teeth, and other sharp, recurved, solid teeth are 

 attached to the under-surface of the anterior moiety of 

 the pterygoid. 



When the moiith is shut, the axis of the quadi'ate bone 

 is iuclined downwards and backwards. The pterygoid, 

 thi-own as far back as it can go, straightens the pterygo- 

 palatine joint, and causes the axes of the palatine and 

 pterygoid bones to coincide. The transverse, 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, to look 

 backwards. Hence these fangs lie along the roof of the 

 mouth, concealed between folds of the mucoiis membrane. 

 But, when the animal opens its mouth for the purx)ose of 

 striking its prey, the digastric muscle, pulling up the angle 

 of the mandible, at the same time thrusts the distal end 

 of the quadi'ate bone forwards. This necessitates the 

 pushing forward of the pterygoid, the result of which is 

 twofold: firstly, the bending of the pterygo-palatine joint; 

 secondly, the partial rotation of the maxillary upon its 

 lachrymal joint, the hinder edge of the maxiUary being 

 thrust downwards and forwards. In virtue of this rota- 

 tion of the maxillary, through about a quarter of a circle, 

 the dentigerous face of the maxilla looks downwards, and 

 even a little forwards, instead of backwards, and the fangs 

 are erected into a vertical position. The snake " strikes ;" 

 by the simultaneous contraction of the crotaphite muscle, 

 part of which extends over the poison-gland, the poison 

 is injected into the wound through the canal of the fang ; 

 and, this being withdrawn, the mouth is shut, all the pre- 

 vious movements are reversed, and the parts return to 

 their fii'st position. 



No Ophidian possesses any trace of anterior extremities, 

 Init the Typhlopidoe, the Pythons, Boas, and Tortrices. have 



