TEE SAUROPSIDA. 101 



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

 adult. 



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

 ■whole, of life. 



10. There is no thoracic diaphragm. 



11. The urinary organs are permanent Wolffian bodies. 

 13. 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 vertebrre 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 always 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 always 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 Mam- 

 malia, 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 belongs to the right side. 



9. Respiration is never effected by means of branchiae, 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 



