XXIIl] 



OPHIDIA 



587 



of the others is that of the IGUANIDAE. These animals have 

 short thick tongues and overlapping scales which form a crest of 

 spines on the head and back and round the throat. Phrynosoma 

 douglasi, the horned "toad," is found all through the Central 

 States and even penetrates into Ontario ; it is the sole Lizard 

 found in Eastern Canada. 



Fm. 290. Dorsal (to the left) and ventral (to the right) views of the skull of the 

 Common Snake, Tropidonotus natrix. After Parker. 



1. Premaxillae (fused). 2. Anterior nares. 3. Nasal. 4. Prefrontal. 

 5. Frontal. 6. Parietal. 7. Maxilla. 8. Transverse bone. 



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. Occip- 

 ital 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. 



Sub-order 2. Ophidia. 



The Ophidia, or true Snakes according to definition, have the 

 right and left halves of the mandible connected by an elastic band ; 

 they are also devoid of a urinary bladder and of any trace of a 

 pectoral girdle. Besides this however they have a large number 

 of other characters which severally are shared by some families 

 of Lizards but which collectively are found only in the Ophidia. 



The vertebrae in addition to the zygapophyses on the sides 

 of the neural arch have median bosses and pits by which they 

 fit into one another, called respectively zygantra and zygo- 

 sphenes (Gr. avr/oov, a cave or hollow; cr<f>ijv, a wedge). There 



