28 GENERAL ANATOMICAL CHARACTERS 
Pig, which we generally write as 14, ¢+, p4, m%. Such a 
generalised formula will admit of modification into that of all 
existing, and a large number of fossil Marsupials, but it is possible 
that some of the Mesozoic types may have had more than four 
premolars, although there is no absolutely decisive evidence that 
such was the case. The presence of seven or eight true molars in 
some Mesozoic forms merely entails the addition of two or three 
additional figures to the ideal generalised formula. 
The milk-dentition of all known Marsupials, existing or extinct, 
is (if not entirely absent) limited to a single tooth on either side of 
each jaw, this being the predecessor of the last permanent premolar. 
And if the view that the milk-dentition is an additional series 
grafted upon the original permanent series be correct, it is evident 
that we have in this single replacement the first stage of this 
additional development. 
In very few mammals are teeth entirely absent. Even in the 
Whalebone Whales their germs are formed in the same manner 
and at the same period of life as in other mammals, and even 
become partially calcified, but they never rise above the gums, 
and completely disappear before the birth of the animal. In some 
species of the order Edentata, the true Anteaters and the Pangolins, 
no traces of teeth have been found at any age. The adult 
Monotremata are likewise devoid of teeth of the same structure 
as those of ordinary mammals; but well-developed molars occur in 
the young Ornithorhynchus, although no traces of teeth have hitherto 
been detected in Echidna. 
Modifications of the Teeth in Relation to their Functions.—The 
principal functional modifications noticed in the dentition of 
mammalia may be roughly grouped as piscivorous, carnivorous, 
insectivorous, omnivorous, and herbivorous, each having, of course, 
numerous variations and transitional conditions. 
The essential characters of a piscivorous dentition are best 
exemplified in the Dolphins, and also (as modifications of the 
carnivorous type) in the Seals. This type consists of an elongated, 
rather narrow mouth, wide gape, with numerous subequal, conical, 
sharp-pointed, recurved teeth, adapted simply to rapidly seize, but 
not to divide or masticate, active, slippery, but not powerful prey. 
All animals which feed on fish as a rule swallow and digest them 
entire, a process which the structure of prey of this nature, especially 
the intimate interblending of delicate, sharp-pointed bones with the 
muscles, renders very advantageous, and for which the above- 
described type of dentition is best adapted. 
The carnivorous type of dentition is shown in its most specialised 
development among existing mammals in the Felide. The function 
being here to seize and kill struggling animals, often of large size 
and great muscular power, the canines are immensely developed, 
