1. premaxillae (fused). 2. anterior nares. 3. nasal. 4. prefrontal. 5. frontal. 6. parietal. 7. maxillae. 8. transpalatine. 9. palatine. 10. pterygoid. 11. pro-otic. 12. exoccipital. 13. supra-occipital. 14. opisthotic. 15. epi-otic. 16. quadrate. 17. parasphenoid. 18. basisphenoid. 19. basi-occipital. 20. occipital condyle. 21. splenial. 22. dentary. 23. angular. 24. articular. 25. supra-angular. 26. coronoid. 27. vomer. 28. squamosal. IX, X foramina for the ninth and tenth cranial nerves.] The disposition of the bones of the jaws is subject to much modification in the Ophidia in order to adapt them for swallowing very large prey. The arrangements again differ greatly in the venomous and non-venomous snakes. In the non-venomous snakes, such as _Python_ and _Tropidonotus_, the palatine is large and is fixed to the pterygoid which extends outwards (fig. 51, 10) so as to be united to the quadrate, and is at the same time firmly connected by the transpalatine with the maxillae. The quadrate is united to the squamosal, which is loosely attached to the cranium. The premaxillae is moderately developed and bears teeth, and the maxillae forms a long bar loosely connected with the rest of the skull. The rami of the mandible are united only by an extremely elastic ligament. It is as regards the maxillae and premaxillae that the skulls of venomous and non-venomous snakes differ most. In the rattlesnake (_Crotalus_) and other venomous snakes the premaxillae is extremely small and toothless. The maxillae is small and subcylindrical, and is movably articulated to the lachrymal, which also is capable of a certain amount of motion on the frontal. The maxillae is connected by means of the transpalatine with the pterygoid, which in its turn is united to the quadrate. When the mouth is shut the quadrate is directed backwards, and carrying back the pterygoid and transpalatine pulls at the maxillae and causes its palatal face, to which the poison teeth are attached, to lie back along the roof of the mouth. When the mouth opens the distal end of the quadrate is thrust forward, and this necessitates the pushing forward of the pterygoid and transpalatine, causing the tooth-bearing surface of the maxillae to look downwards and the tooth to come into the position for striking. The Ophidian skull is also noticeable for the absence of the jugals and quadratojugals. In poisonous snakes the place of the jugal is taken by the zygomatic ligament which connects the quadrate and maxillae.