102 THE ANATOMY OF YERTEBRATED ANIMALS. 



11. The Wolffian 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, whicb presents a uterine dilata- 

 t ion in the lower part ot 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 

 vi tell us of the egg. 



IG. There are no mammary glands. 



III. — The Mammalia 



1. Always possess an epidermic exoskeleton in the form of 

 hairs. 



2. The vertebras are ossified, and (except in the ornitho- 

 delphici) their centra have terminal epiphyses. 



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

 fied. No distinct parasphenoid exists in the adult. TheproStic 

 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 with 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 brancliia3, but, 

 after birth, is performed by lungs. 



10. There is a complete diaphragm. 



11. The Wolffian bodies are replaced by permanent kidneys. 



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

 losum. 



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

 cloaca. Tlie oviduct is a Fallopian tube. 



