724 MAMMALIA. 
The typical mammalian dentition already referred to may be expressed 
as follows :— 
Incisors 33, canines = premolars 4—4, molars 3—3 = 227" = total, 445 
3-3 4- 3° «I-11 
or, using initial fevers 
303 0 Ia 4-4 3-3_ 
i. Spt por PM mas 
or, recognising that the right and left side are almost invariably identical, 
and omitting the initial letters— ar 
The formulz for the adult dentition of some representative Mammals 
are the parent — 
Opossum = be +, Thylacine * = 4) Kangaroo 25 ots 4) Wombat nae , Pig == 3143 , Camel eas, 
413 = ay 3143" 3123 
Sheep 33 ser Horse ele ey Rabbit on Cat on Dog 374?, Bear 247, Seal 3247, 
3143” gran’ 3143 35 43° 214r’ 
cient ‘ et , Marmoset = 2732 2, New ar Monkey 2793, Old World Monkey > 
Man 2123. 
2123 
It is interesting to note the relation in particular cases between the 
diet and the form of the teeth. Thus the dolphins, which feed on fish 
and swallow them whole, have numerous, almost uniform, sharp, 
recurved, conical teeth, well suited to take a firm grasp of the ‘slippery 
and struggling booty. Toa slight extent the same piscivorous dentition 
may be seen in seals, In the more strictly carnivorous Mammals the 
incisors are small, the canines are long and sharp, piercing the prey 
with a deathful grip, while the back teeth have more or less knife-like 
edges, which sever flesh and bone. In typical insectivorous Mammals 
the upper and lower incisors meet precisely, ‘‘so as readily to secure 
small active prey: quick to elude capture but powerless to resist when 
once seized,” while the crowns ‘of the molars bear many sharp points. 
Herbivorous Mammals have front teeth suited for cropping the herbage 
or gnawing parts of plants, the canines are small or absent, the molars 
have broad grinding crowns with transverse ridges. In omnivorous: 
Mammals the incisors are suited for cutting; the canines are often 
formidable weapons in the male sex; the molars have crowns raised 
into rounded tubercles. 
A primitive form of tooth with three cusps in one plane is called 
triconodont ; when the three cusps form a triangle, the tooth is called 
tritubercular ; when the crown has a number of blunt or pointed cusps, 
it is called bunodont ; when the cusps run into ridges, the term /ophodont 
is used ; when the cusps form a crescent, the tooth is called selenodont ; 
when there is a long crown with the neck (the junction region between 
crown and root) deep in the socket, the tooth is called Aypsodont ; 
when there is a short crown with the neck at the surface of the gum, the 
term drachyodont is used. 
Development and placentation.—The ova of Mammals, 
except Monotremes, are small; even those of the Whales are 
