ORGANS OF DIGESTION. Eid 
that it is larger and presents an anterior basal cusp in addi- 
tion to the others. The lower molar, sometimes called the 
sectorial, because it shears against the upper sectorial or 
carnassial premolar, presents two nearly equal cusps, the 
protoconid and the paraconid. The root consists of two 
fangs, the anterior of which is the larger. 
The deciduous or milk teeth begin to appear above the 
gums when the kitten is two weeks old. The incisors and 
the canine appear first, then the second and third molars. 
The first upper molars do not appear till the kitten is about 
six weeks old. According to Jayne, the deciduous dentition 
is complete at the end of the second month. At the end of 
the fourth month the milk incisors are being displaced by 
the permanent teeth. The formula for the temporary set 
is di %, dc 4%, dm *. 
Teeth are present in nearly all adult mammals. The 
whalebone whales, the duck-bill, and some of the ant-eaters 
have no teeth in the adult state, but teeth are present during 
their embryonic life. The Echidna shows no evidence of 
teeth at any time. Most mammals have two distinct sets of 
teeth, known as the milk or deciduous set, and the perma- 
nent set. In the Marsupialia, ‘the milk dentition is in a 
degenerate condition. The milk teeth are present, but none 
become sufficiently developed to appear above the gums, ex- 
cept the last premolar, and in some cases the canine and the 
incisors. The sloths have only one set of teeth and are 
therefore Monophydont. Mammals having both a milk and 
a permanent set are termed Diphydont. 
In the majority of mammals the teeth are divided accord- 
ing to form and function into four groups: incisors, 
canines, premolars, and molars. Such a dentition is known 
as Heterodont, in distinction to the Homodont dentition, 
in which all the teeth have the same form, as is the case in 
the dolphins. In mammals with a heterodont dentition the 
