7o6 



PHYLUM CHORDATA : CLASS REPTILIA 



separation of the mandibles from the base of the skull." 

 The nasal region may also be movable. On the other hand, 

 the bones of the brain-case proper are firmly united. The 

 premaxillae are very small and rarely bear teeth ; the 

 palatines are usually connected ^Yith the maxillae by trans- 

 verse bones, and through the pterygoids with the movable 

 quadrates. 



Teeth, fused to the bones which bear them, occur on the 

 dentaries beneath, and above on the maxillae, palatines, 

 and pterygoids, and very rarely on the premaxillae. The 



PMX 



N PftF PR PF 



^TVl X PTY 



Fig. 416. — Side view of skull of non-poisonous Pythonid snake. 



—From a Specimen. 



PMX., Premaxilla ; N., nasal ; PRF.; pre-frontal ; FR., frontal 

 above orbit; PF., post-frontal; PA., parietal; PER., periotic ; 

 SQ., squamosal ; Q., movable quadrate ; AR., articular of lower 

 jaw; PTY., pterygoid; PL., palatine, fused to pterygoid; 

 A., angular of lower jaw ; PL., palatine ; D., dentary of lower 

 jaw ; MX., maxilla. Teeth occur on maxilla and dentary, and a 

 few on the front part of the fused palato-pterygoid. A short 

 OS transversum runs from the palatine to the maxMla. 



fang-like teeth of venomous serpents are borne bv the 

 maxillae, and are few in number. Each fang has a groove 

 or canal down which the poison flows. When the func- 

 tional fangs are broken, they are replaced by reserve fangs 

 which lie behind them. In the egg-eating African Dasy- 

 peltis the teeth are rudimentary, but the inferior spines of 

 some of the anterior vertebrae project on the dorsal wall of 

 the gullet, and serve to break the egg-shells. 



When a venomous snake strikes, the mandible is lowered, 

 the distal end of the quadrate is thrust forward (this pushes 

 forward the pterygoid), the pterygo-palatine joint is bent. 



