THE SAUEOPSIDA. 113 



6. The alimentary canal may or may not terminate in a 

 cloaca. When there is no cloaca the rectum opens in front 

 of the urinary organs. 



7. The blood-corpuscles are always nucleated, and the 

 heart may be tubular, bilocular, or trilocular. 



8. There are never fewer than two aortic arches in the 

 adult. 



9. Respiration takes place by branchiae during part, or 

 the whole, of life. 



10. There is no thoracic diaphragm. 



11. The iirinary organs are permanent Wolffian bodies. 



12. The cerebral hemispheres may be absent, and are 

 never united by a corpiis callosum. 



13. The embryo has no amnion, and, at most, a rudi- 

 mentary allantois. 



14. There are no mammary glands. ' 



II. — The Sauropsida 



1. Almost always possess an epidermic exoskoleton in the 

 form of scales or feathers. 



2. The centra of the vertebrae are ossified, but have no 

 terminal epiphyses. 



3. The sktdl has a completely ossified occipital segment, 

 and a large basisphenoid. No separate parasphenoid exists 

 in the adult. The pro-otic is always ossified, and either 

 remains distinct from the epiotic and opisthotic through- 

 out Ufe, or unites with them only after they have anky- 

 losed with adjacent bones. 



4. There is always a single, convex, occipital condyle, into 

 which the ossified ex-occipitals and basi-occipital enter in 

 various proportions. 



5. The mandible is always present, and each ramus con- 

 sists of an articular ossification, as well as of several mem- 

 brane bones. The articular ossification is connected with 

 the skull by a quadrate bone. The apparent " ankle-joint " 

 is situated, not between the tibia and the astragalus, as in 

 all Mammalia, but between the proximal and the distal divi- 

 sions of the tarsus. 



I 



