718 MAMMALIA [Cfl. 



Sub-class II. METATHERIA. 



Mammalia in which the young are born in a most imperfect 

 condition, and are carried by the mother in a pouch on the 

 abdomen. The oviducts are differentiated into vagina, uterus 

 and Fallopian tube and the two vaginae are partially united. The 

 cloaca is divided into an anus and a urino-genital aperture. An 

 allaritoic placenta may or may not be developed but when present 

 is more or less vestigial. In all cases there is an umbilical placenta 

 consisting of an adhesion between the yolk-sac of the embryo and 

 the uterus. 



Order I. Polyprotodontia. 



Metatheria with four or five incisors on each side of the 

 upper jaw and with at least three pairs of incisors of approxi- 

 mately equal size in the lower jaw. 



Family 1. Didelphyidae. 



Polyprotodontia with a large opposable great toe, the 

 other digits of the hind-foot being subequal in size. 

 American. 



Ex. Didelphys. 



Family 2. Dasyuridae. 



Polyprotodontia with a rudimentary great toe, the other 

 digits of the hind-foot subequal in size. Australian. 

 Ex. Thylacinus. 



Family 3. Peramelidae. 



Polyprotodontia with a rudimentary great toe, the 

 other digits of the hind-foot united by a web of skin, the 

 second and third being excessively slender : the muzzle 

 long and pointed. Australian. 



Ex. Perameles. 



9 



Family 4. Notoryctidae. 



Polyprotodontia with rudimentary eyes, an enlarged 

 manus and burrowing habits. Australian. 

 Ex. Notoryctes. 



Order II. Diprotodontia. 



Metatheria with not more than three incisors on each side 

 of the upper jaw, and with, as a rule, one pair of large chisel- 

 shaped incisors in the lower jaw, the other lower incisors being 

 vestigial or absent. 



