(a) Eutheria, Monodelphia, or Placentals those in which there is a 



close (placental) union between the unborn embryo and its 



mother, e.g. Ungulates, Carnivores, Monkeys. 

 (/;) Metatheria, Didelphia, or Marsupials the prematurely bearing. 



usually pouch -possessing kangaroos, opossums, etc. 

 (c) Prototheria, Ornithodelphia, or Monotremes - - the egg-laying 



duckmole (Ornilkorkynchus), Echidna, and Proechhina. 



FIG. 2. Phenacodus, a primitive extinct Mammal. After Cope. 



Birds. --There can be 

 no hesitation as to the 

 class which ranks next to 

 Mammals. For Birds are 

 in most respects as highly 

 developed as Mammals, 

 though in a different direc- 

 tion. They are character- 

 ised by their feathers and 

 wings, and many other 

 adaptations for flight, by 

 their high temperature, 

 by the frequent spongi- 

 ness and hollowness of 

 their bones, by the tend- 

 ency to fusion in many 

 parts of the skeleton, 

 by the absence of teeth 

 in modern forms, by 

 the fixedness of the 

 lungs and their associa- 

 tion with numerous air sacs, and so on. 



FIG. 3. Extinct moa and modern 

 kiwi. After Cams Sterne. 



