1 VESTIGIAL TEETH 45 
due the complicated patterns upon the grinding teeth of Ungulates, 
which are produced by the wearing away of the dentine and the 
cement, and the resistance of the enamel. 
The centre of the tooth papilla remains soft and forms the 
pulp of the tooth, which is continuous with the underlying 
tissues of the gum by a fine canal or a wide cavity as the case 
may be. In teeth which persistently grow throughout the life- 
time of the animal, as for example the incisors of the Rodents, 
there is a wide intercommunication between the cavity of the 
tooth and the tissues of the gum; only a narrow canal exists in, 
for instance, the teeth of Man, and in fact in the vast majority 
of ‘cases. The three constituents of the typical teeth are not, 
however, found in all mammals; the layer which is sometimes 
wanting is the enamel. This is the case with most Kdentates ; 
but the interesting discovery has been made (by Tomes) that in 
the Armadillo there is a downgrowth of the epidermis similar to 
that which forms the enamel in other mammals, a rudimentary 
“enamel organ.” 
Teeth are present in nearly all the Mammalia; and where 
they are absent there is frequently some evidence to show that 
the loss is a recent one. The Whalebone Whales, the Mono- 
tremata, Manis, and the American Anteaters among the Edentata 
are devoid of teeth in the adult state. In several of these 
instances, however, more or less rudimentary teeth have been 
found, which either never cut the gums or else become lost 
early in life. The latter is the case with Ornithorhynchus, 
where there are teeth up to maturity (see p. 115). Kiikenthal 
has found germs of teeth in Whales, and Rose in the Oriental 
Manis. The loss of the teeth in these cases. seems to have 
some relation to the nature of. the food. In ant-eating 
mammals, as in the Anteaters and Hchidna, the ants are 
licked up by the long and viscid tongue, and require no 
mastication. Yet it must be remembered that Ovrycteropus 1s 
also an anteater, like the Marsupial Myrmecobius, both of which 
genera have teeth. 
The first’ of the essential peculiarities of the mammalhan 
teeth as compared with those of other vertebrates concerns the 
position of the teeth in the mouth. There is no undoubted 
mammal extinct or living in which the teeth are attached to 
co) 
any bones other than the dentary, the maxilla, and the pre- 
