CHAPTER XXIX 



REPTILIA 

 (By Leo T. Murray and James E. Blaylock) 



Class Beptilia includes among living- forms, turtles, snakes, lizards, 

 alligators, and similar animals. These are the only living vertebrates 

 which are cold blooded, breathe by lungs, and have a single median 

 occipital condyle. A more complete list of distinguishing charac- 

 teristics has been given by Gadow as follows: 



"1. The vertebrae are gastroceutrous. 



"2. The skull articulates with the atlas by one condyle, which is 

 formed mainly by the basioccipital. 



"3. The mandible consists of many pieces and articulates with the 

 cranium through the quadrate bones. 



"4. There is an auditory columellar apparatus fitting into the 

 fenestra ovalis. 



"5. The limbs are of the tetrapodous, pentadactyl type. 



"6. There is an intracranial hypoglossal nerve. 



"7. The ribs form a true sternum. 



"8. The iliosacral connection is postacetabular. 



"9. The skin is covered (a) with scales, but (b) neither with 

 feathers nor with hairs ; and there is a great paucity of glands. 



"10. Reptiles are poikilothermos (cold blooded). 



"11. The red blood corpuscles are nucleated, biconvex, and oval, 



' ' 12. The heart is divided into two atria and an imperfectly divided 

 ventricle. It has no conus, but semilunar valves exist at the base 

 of the tripartite aortic trunk. 



"13. The right and left aortic arches are complete and remain 

 functional. 



' ' 14. Respiration is effected by lungs ; functional gills are entirely 

 absent, even during embryonic life. 



"15. Lateral sense organs are absent. 



"16. The metanephric kidneys have no nephrostomes. Each kidney 

 has one separate ureter. 



"17. There is always a tj^ical cloaca. 



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