i02 THE ANATOMY OF VEETEBRATED ANIMALS. 



11. The AYolffian bodies are replaced, functionally, by per* 

 manent 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 a uterine dilata- 

 tion in the lower part of its course. 



14. All are oviparous, or ovoviviparous. 



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

 allantois, and is developed at the expense of the massive 

 vitellus of the egg. 



10. There are no mammary glands. 



III. — The Mammalia 



1. Always possess an ej)idermic exoskeleton in the form of 

 hairs. 



2. The vertebrge are ossified, and (except in the ornitliO' 

 delphid) their centra have terminal epij)hyses. 



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

 fied. No distinct parasphenoid exists in the adult. Tiie prootic 

 ossifies, and unites with the epiotic and opisthotic 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 wdth the squamosal. The quadrate bone, 

 and the supra-stapedial element of the hyoidean arch, are con- 

 verted into a malleus and an incus, so that, with the stapes, 

 there are, at fewest, three ossicula audiMs. 



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

 cloaca. When it does not, the rectum opens behind the 

 genito-urinary organs. 



7. The heart is quadrilocular. Some of the blood-cor- 

 puscles are always red and non-nucleated. 



8. There is only one aortic arch which lies on the left side. 



9. Respiration is never effected by means of branchia?, but, 

 after birth, is performed by lungs. 



10. There is a complete diaphragm. 



11. The Wolffian bodies are rejDlaced by permanent kidneys. 



12. The cerebral hemispheres are united by a corpus cal- 

 losum. 



13. The reproductive organs may, or may not, open into a 

 cloaca. The oviduct is a Fallopian tube. 



