184 MAMMALIAN DESCENT. [Lficr. VII. 



the ordinary annulus (tympanic or proper bone of the 

 drum). 



3. Besides an anticipation of the carnivorous type of 

 skull, there are plain and evident memorials of that 

 of the Marsupial ; for the ali-sphenoids each give off a 

 trumpet-shaped process to enlarge the cavum tympani 

 or cavity of the ear-drum ; a most diagnostic character 

 in the Metatheria. 



4. I have already spoken of a very peculiar structure 

 seen in many of the Australian Marsupials, namely, that 

 the posterior paired vomers are large, for they meet 

 behind the moderate-sized middle-piece ; this is well 

 seen in Rhynchocyon ; there are several more characters 

 equally marsupial. 



5. The very diagnostic tympanic wings of the basi- 

 sphenoid are absent in this peculiar Insectivore. 



6. The pre-sphenoid or third basal beam-bone is 

 distinct, as in Marsupials and Rodents. 



Thus this greatly specialised kind of Insectivore, whilst 

 retaining the most marked characteristics of the Meta- 

 therian skull, takes on two characters, one of which, had 

 it become dominant, would have landed it amongst the 

 Proboscidea or Elephants, whilst the other would have 

 made it a Carnivore. It attempted too much at once, 

 and thus, like a man in doubt, it made but little progress ; 

 moreover, in this developmental shilly-shallying, it failed 

 to drop the old Marsupial, to take on the new Eutherian, 

 nature, and was thus in danger of going out of being 



