1854.] OF THE ROYAL INSTITUTION. BE: 
a diminished number and an altered position of the incisors. One 
sees, indeed, in the carnivorous series, that a corresponding de- 
crease in the number of the premolars is concomitant with the 
shortening of the jaws. Already in the Mustelide, the first pre- 
molar below is abrogated; in Felis also above, with the further 
loss of the second premolar in the lower jaw; the true molars 
being correspondingly reduced in these strictly flesh-eating ani- 
mals, but taken away from the back part of their series. 
If we were desirous of further testing the soundness of the 
foregoing conclusions as to the nature of the teeth absent in the 
reduced dental formula of man, we ought to trace the mode in 
which the type is progressively resumed in descending from man 
through the order most nearly allied to our own. 
Through a considerable part of the Quadrumanous series, e. g. 
in all the Old World genera above the Lemurs, the same number 
and kinds of teeth are present as in man ; the first deviation being 
the disproportionate size of the canines and the concomitant break 
or ‘diastema” in the dental series for the reception of their 
crowns when the mouth is shut. This is manifested in both the 
Chimpanzees and Orangss, together with a sexual difference in the 
proportions of the canine teeth. Then comes the added pre- 
molar in the New-World Monkeys, and the further additions in 
lower quadrupeds, until in the Hog genus we see the old primi- 
tive type of Diphyodont dentition resumed or retained. 
With regard to the application of the above principles and 
characters to other or newly discovered species:—When the 
premolars and the molars are below their typical number, the 
absent teeth are missing from the fore-part of the premolar series 
and from the back part of the molar series. The most constant 
teeth are the fourth premolar and the first true molar; and, these 
being known by their order and mode of development, the homo- 
logies of the remaining molars and premolars are determined by 
counting the molars from before backwards, e.g. “ one,” ‘ two,” 
“three ;” and the premolars from behind forwards, “ four,” 
“ three,” “ two,” “ one.” The incisors are counted from the 
median line, commonly the foremost part of both upper and lower 
jaws, outwards and backwards. The first incisor of the right 
side is the homotype, transversely, of the contiguous incisor of 
the left side in the same jaw, and, vertically, if its opposing tooth 
in the opposite jaw; and so with regard to the canines, pre- 
molars, and molars ; just as the right arm is the homotype of 
the left arm in its own segment, and also of the right leg of a 
succeeding segment. It suffices, therefore to reckon and name 
the teeth of one side of either jaw in a species with the typical 
number and kinds of teeth; e. g. the first, second, and third in- 
cisors,—the first, second, third, and fourth premolars,—the first, 
second, and third molars; and of one side of both jaws in 
any case. 
