THE SAUEOPSIDA. 101 



8. There are never fewer tlian two aortic arclies in the 

 adult. 



9. Respiration takes place by branchiae during part, or the 

 whole, of life. 



10. There is no thoracic diaphragm. 



11. The urinary organs are permanent Wolffian bodies. 



12. The cerebral hemispheres may be absent, and are 

 nev^er united by a corpus callosum. 



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

 tary allantois. 



14. There are no mammary glands. 



II. — The Sauropsida 



1. Almost always possess an epidermic exoskeleton in the 

 form of scales or feathers. 



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

 terminal epiphyses. 



3. The skull has a completely ossified occipital segment, 

 and a large basisphenoid. No separate parasphenoid exists 

 in the adult. The prootic is ahvays ossified, and either 

 remains distinct from the epiotic and opisthotic throughout 

 life, or unites with them only after they have anchylosed with 

 adjacent bones. 



4. There is alwa^^s a single, convex, occipital condyle, into 

 which the ossified ex-occipitals and basi-occiptal enter in vari- 

 ous 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 situ- 

 ated, not between the tibia and the astragalus, as in all 3Iani- 

 inalia^ but between the proximal and the distal divisions of 

 the tarsus. 



6. The alimentary canal terminates in a cloaca. 



7. The heart is trilocular or quadrilocular. Some of the 

 blood-corpuscles are always red, oval, and nucleated. 



8. The aortic arches are usually two or more, but may be 

 reduced to one, which then belons-s to the rioht side. 



■ • • • ^ 



9. Respiration is never effected by means of branchire, but, 

 after birth, is performed by lungs. The bronchi do not branch 

 dichotomously in the lungs. 



10. A thoracic diaphragm may exist, but it never forms 

 a complete partition between the thoracic and the abdominal 

 viscera. 



