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 Eodents, 

 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 Edentates ; 

 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 JMainmalia ; 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 Ornitlwrhyiichus, 

 where there are teetli up to maturity (see p. 113). Kiikenthal 

 has found germs of teeth in Whales, and Eose in the Oriental 

 3£anis. 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 Echidna, the ants are 

 licked up by the long and viscid tongue, and require no 

 mastication. Yet it must be remembered that Orycterojms is 

 also an anteater, like the Marsupial MyrmecoMus, both of which 

 genera have teeth. 



The first of the essential peculiarities of the mammalian 

 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 

 any bones other than the dentary, the maxilla, and the pre- 



