THE TEETH OF MARSUPIAL1A. 421 



That is to say, though the total number of teeth is the 

 same, the marsupial has only three premolars and has four 

 true molars. The premolars (false molars) differ from the 

 true molars in the greater simplicity of their crowns, just as 

 in most placental mammals ; but, although, looking at the 

 complete adult dentitions, no hesitation would be felt in 

 classing the teeth under the heads of premolars and true 

 molars, yet there is a curious anomaly in the succession of 

 the teeth which applies to the whole of the sub-class Mar- 

 supialia, and to some extent invalidates the definition of 

 " premolar " as applied to their teeth. Only one of the 

 premolars (the hindmost) has vertically displaced a milk 

 tooth ; indeed, the whole milk dentition of Marsupials con- 

 sists of four milk molars (one on each side of each jaw), 

 there being no milk incisors nor canines in any known 

 marsupial. It is further pointed out by Professor Flower, 

 who was the first to fully describe these peculiarities in the 

 succession of marsupial teeth (" Phil. Trans.," 1867), that the 

 extent to which the solitary milk molar is developed varies 

 much in the different families j no trace of any succession 

 has been observed in the Wombat ; in the Thylacine (a dog- 

 like creature) the small milk molar is calcified, but is 

 absorbed or shed prior to any other teeth being erupted, 

 whilst in the Kangaroos it is retained till a much later 

 period (see page 430), and in the Kangaroo Pvat (Hyp- 

 siprymnus) the milk molar has not yet given place to its 

 successor at the time when the last permanent molar has 

 come into place, so that it for a long time ranges with the 

 other teeth and does work. It is difficult to obtain very 

 young Marsupials, and material for the complete elucidation 

 of the subject is wanting ; but I have had the opportunity 

 of making sections of the jaws of several young specimens 

 ( Perameles and Halmaturus), taken from the pouch by my 

 Iriend Prof. Moselcy, and I have not so for succeeded in 



