SUCCESSION OF THE TEETH IN THE DASYURIDiE. 
455 
by Otocyon* viz., three incisors and one canine, all changing ; four premolars, of which 
the last three change; and four molars. Finally, IX. is the still further development 
shown in the Tapir, Hyrax, and one or two other forms, in which pm 1 also changes, 
and, as in the vast majority of Placental Mammals, m 4 is lost. 
If, now, we attempt in the same manner to trace the history of the tooth-changes 
upwards to the earlier forms from the Marsupial dentition, instead of downwards to 
the later ones, we obtain a diagram as follows :— 
Here IV. is, as before, the generalised Marsupial dentition, as already described. 
III. would then be the stage preceding it, where one or more additional posterior 
molars are still habituall} 1- retained, and where the milk predecessor to pm 4 has not yet 
been developed, although that tooth is in the preliminary stage of retardation. In 
II. we get back to a condition in which the teeth are about equal to one another in 
I. 
II. 
III. 
IV. 
Premaxillary teeth. 
r \ 2 3 4 5 
V V V V V 
I 
^ 
12 3 4 5 
V V V V V 
V V V V V 
V V V V v 
Fig. 3. 
Maxillary teeth. 
1 23456789 10 
VVVVVVVVVV&C. 
I I 
P M 
A« 
n r 
2 3 4 1 
M 
V 
2 3 4 5 
V V V V I_II_11_II_II_I 
V 
V V V 
V 
I_II_II_II_11_I 
V 
V V V 
V 
UU UU o 
their rate of development, none being retarded, and only show a commencement 
or first sketching out of the division into canines,! premolars, and molars by a 
lengthening of the anterior and a broadening of several of the posterior maxillary 
teeth. Finally, in I. the teeth would have been of a purely homodont character, only 
divisible into five premaxillary and a variable number of maxillary teeth. Of these 
maxillary teeth, it would seem to have been generally the fifth (= pm 4 ) which first 
developed a milk predecessor, and thereby became, with the three non-caniniform teeth 
in front of it, a “ premolar.” Where the maxillary teeth exceeded nine, the increase 
* Whether this animal has returned to, or retained, its ancestral number of molars is still doubtful, 
but it presents, in any case, an interesting example of a stage of dentition through which the line of 
Placental Mammals must have passed. (Gf. Huxley, ‘ Zool. Soc. Proc.,’ 1880, p. 256 et seq .) 
f Although, as urged by Moseley and Lankestek (‘ Journ. Anat. Physiol.,’ vol. 3, 1869, p. 73), the 
canine is not essentially a distinct tooth from the premolars, yet it was evidently very early specialised, 
as is shown by such forms as the Mesozoic Stylodon pusillus, Owen. 
