114 THE ANATOMY OF VERTEBEATED ANIMALS. 



6. The alimentaiy 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 

 rediiced 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 foi-ms a 

 complete partition between the thoracic and the abdominal 

 viscera. 



11. The Wolffian bodies are replaced, functionally, by 

 permanent kidneys. 



12. The cerebral hemispheres are never united by a corpus 

 callosum. 



13. The reproductive organs open into the cloaca, and 

 the oviduct is a Fallopian tube, which presents an uterine 

 dilatation in the lower part of its course. 



14. All are oviparous,. or ovoviviparous. 



15. The embryo has an amnion, and a large respiratoiy 

 allantois, and is developed at the expense of the massive 

 vitellus of the egg. 



16. There are no mammai-y glands. 



III. — The Mammalia 



1. Always possess an epidermic exoskeleton in the form of 

 hairs. 



2. The vei-tebrse are ossified, and (except in the Ornitho- 

 delphia) their centra have terminal epiphyses. 



3. All the segments of the brain-case are completely 

 ossified. No distinct parasphenoid exists in the adult. 

 The pro-otic ossifies, and unites vnth the epiotic and opis- 

 thotic before these coalesce with any other bone. 



4. There are always two occipital condyles, and the basi- 

 occipital is well ossified. 



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

 sists (at any rate, in the adult) of a single membrane bone, 

 which articulates with the squamosal. The quadrate bone. 



