1010 
Journal of Agricultural Research 
Vol. XXVIII, No. 1ft 
THE TEETH 
The changes that occur in the teeth of microtines soon after birth are exceed¬ 
ingly interesting and significant. As there are no newly born young in the 
present series, however, and data on dentition of this group are being presented 
in another paper under preparation by the author, this subject will not be treated 
in the present contribution. 
Certain teeth, notably the last upper and first lower molars, are exceedingly 
variable, as is the rule in this subfamily. The tooth pattern of microtines is, 
of course, of very great value in diagnosing groups and many of the species. 
In spite of the efforts of many investigators, however, it has proved impossible 
to correlate minor variations either with age or any other character, and it is 
strongly felt that an undue importance has often, if not usually, been attached 
to such differences in enamel pattern in the study of closely related forms. 
There has been the same failure in the present study, and in spite of the author's 
best efforts along this line it has not been possible to assign to these variations 
within the series any significance whatsoever, save that they undoubtedly 
indicate some active, composite, evolutional trends on the part of the teeth 
concerned. 
There is considerable individual variation in the length of the maxillary tooth 
row, with age difference to correspond. The average length for males is 6.68 
Fig. 22. —Diagrammatic iateral aspect of left ramus of the mandible 
of adult skull, a, Coronoid process; 6, temporal fossa; c, masseteric 
ridge; d, condyle; e, incisive process; /, angular process 
mm., with extremes of 7.2 and 6.1, a difference of 1.1 mm., or 16.4 per cent of 
the average. The average for females is, 6.7 mm., with extremes of 7.4 and 
6, a difference of 1.4 mm., or 20.9 per cent. The sexual difference in size in favor 
of the females, although possibly of some significance, is not sufficiently pro¬ 
nounced to be of much value. It is worthy of note, however, that the greater 
variation in this character occurs among the females instead of among males, 
as is usual in the case of most measurements. The size of the alveoli increases 
with general growth of the skull; hence the individual teeth are broader in both 
the antero-posterior and lateral dimensions in adults. The alveolar width, 
greatest distance between the lateral borders of the tooth rows, shows less 
individual variation, but almost as much variation with age as the length of 
tooth row. To a slight extent only is it correlated with the latter. In males 
it averages 5.61 mm., with extremes of 6.1 and 5.3, a difference of 8 mm., or 
14.3 per cent. In females it averages 5.52 mm., with extremes of 6 and 5.4, 
a difference of 0.6 mm., or 10.8 per cent. In this character the greater size, as 
well as variation, occurs among males. 
Variation in molar pattern is not by any means always bilaterally symmetrical, 
although corresponding teeth upon the two sides usually exhibit similar trends. 
There is no appreciable variation in the amount of dentine occurring within the 
