TEETH AND THE ALLIED ORGANS IN MAMMALIA.' 283 
the alveolar periosteum. Absorption is effected by means of 
a large number of cells developed on the surface of the root ; 
and this goes on till the whole root is removed. At the same 
time, the bony septum between the temporary and permanent 
teeth is absorbed, and the milk-tooth drops out. In some 
instances, the milk-teeth remain with their roots scarcely 
diminished, while the permanent teeth are taking their 
place. 
The permanent teeth are connected with the milk-teeth 
only, as described, through the enamel-organ : in all other 
respects, they are quite independent. A milk-tooth may be 
entirely wanting ; and yet the permanent tooth which should 
replace it will appear at the proper time. 
With regard to the precise relations of the temporary to the 
permanent tooth, opinions are not as yet settled. Owen 
holds that the permanent true molars are a continuation back- 
wards of the milk-series. Mr. Flower, however, dissents from 
this. In animals which have the milk-teeth functionally de- 
veloped, these are an epitome of the permanent set; the last 
milk-tooth being a copy of the last permanent tooth ; and, in 
placing the two sets side by side, we see a break in the tem- 
porary molar series. Again, where the milk-teeth are only 
rudimentary, it is difficult to believe the last molars to belong 
to that series. The Marsupials have only one small temporary 
tooth on each side of the jaw ; in a young Thylacine, this 
has been found about to be shed when all the other (perma- 
nent) teeth were developed. It is difficult, then, to avoid the 
conclusion that the last true molars belong to the permanent 
set. 
While there are several instances in which the milk-teeth 
are merely rudimentary, the permanent teeth being well 
developed, there is not one known example of the converse. 
The milk-teeth are — if the expression may be used — super- 
added to the permanent set, and belong to a high grade of 
development. 
Nearly all Mammalia have teeth. In Monotremata, they 
are not calcified ; and even in Edentata they are not entirely 
wanting. Cetacea can scarcely be said to have no teeth, in- 
asmuch as even the Whalebone-Whales possess rudimentary 
teeth at some period. 
The number of teeth varies much among the Homodonts. 
The Great Anteater has 98 ; and there is a species of Dolphin 
which has 220 — the largest number that is known. In Diphy- 
odonts or Heterodonts, the typical number is 44 ; and this is 
rarely exceeded. There is a fox-like animal which has 48 ; and 
there are a few instances of excess among Marsupials, some 
