CHORDATA. 195 



Sub-Class III. EUTHERIA (Monodelphia, 

 Placentalia). 



The embryo is nourished by means of an allantoic placenta ; the niar- 

 supium and epipubic bones are absent ; vagina single ; scrotum, when 

 present, behind the penis. Alisphenoid does not form an auditory bulla ; 

 angle of mandible rarely inflected. 



Fossil from the Eocene onwards. 



