BY W. J. McKAY. 973 



is depressed anteriorly, it will move downwards, outwards, and 

 backwards, and by this means a wide gape is attained ; this is 

 aided by the fact that the mandible is concave above from before 

 back. 



AVith regard to the movements of the head on the atlas we have 

 seen that, while downward movement is easy, upward move- 

 ment is limited by the close apposition of the exoccipital to the 

 atlas. This is a decided advantage, for the snake when striking is 

 able to steady its head against the atlas by contracting the dorsal 

 muscles prolonged on to the skull. And again, since the muscles 

 which enable it to strike are attached to processes on the basi- 

 occipital, it follows that the head is acted on like a lever of the 

 second order, the fulcrum being at the anterior face of the atlas ; 

 thus dislocation downwards of the occipital condyle is prevented by 

 resting on the flat surface of the atlas, and by the exoccipifcals 

 meeting the anterior borders of this bone in the manner described 

 above. 



We now come to a point which is of considerable interest. 

 Huxley and many others have described the erection of the fangs 

 as the result of the action of the quadrate on the pterygoid bone, 

 leaving out of the process the action of the s{)ecial muscles which we 

 have described above. Huxley says : — " When the animal opens 

 its mouth for the purpose of striking its prey, the digastric muscle 

 pulling up the angle of the mandible, at the same time thrusts the 

 distal end of the quadrate forward. 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 (pre-frontal) joint, 

 the hinder edge of the maxillary being thrust downwards and 

 forward. In virtue of this rotation of the maxillary through 

 about a quarter of a circle, the dentigerous face of the maxilla 

 looks downwards and even a little forward, instead of backwards, 

 and the fangs are erected into a vertical position." 



While we agree with the above description in regard to the 

 actual movements of the bones, we unhesitatingly say, that the 

 supposed means by which these movements are brought about are 



