THE SKULL 



293 



with it by the intermediary of the squamosal. When a snake 

 opens its mouth the lower jaw drops and the quadrate moves 

 forward. This movement of the quadrate is imparted to the 

 pterygoid and transpalatine bones, which, moving forward in 

 their turn, cause the maxilla and associated bones to rotate 



n pjf. f. R^ 



Fig. 145. — Left side view of the skull of a snake (puff adder) showing the 

 streptostylic condition of the jaws.. A, with the mouth closed ; B, 

 with the mouth open. 



upwards. In some snakes such as the viper, this process of 

 rotation of the maxilla is especially interesting, for the maxilla 

 carries the long teeth which are modified into poison fangs. 

 When the mouth is open these poison-fangs are made to 

 project forwards out of the mouth ready for " striking " ; 

 whereas in the normal position of rest with the jaws closed, 



