54 ORAL EQUIPMENTS. 



powerful. A rat will gnaw through water-pipes in whieh 

 it has heard water bubbling, and a beaver will Ml a consider- 

 able sized tree. 



With this brief explanation of the typical characteristics 

 of these three well specialised classes, which I hope may have 

 been made clear enough to enable you to follow me in what I 

 have to say next, I will proceed to advert to some of the 

 special differentiations of teeth for definite purposes, and here 

 let me say that we shall get much valuable assistance from 

 the really well executed diagrams Mr. T. Caldwell Jones has 

 been good enough to produce for me. 



In referring to this subject, I intend to make a classifica- 

 tion of my own, and not mind sticking closely to text-book 

 classes, as I think I can make the matter more comprehen- 

 sible by referring to the functional conditions of the individual 

 teeth. 



I may say that with a very few exceptions, as for instance 

 the upper carnassial tooth of the " Felidae " which is a pre- 

 molar, and one or two other examples, the specialisation of 

 teeth takes place : 1, In the incisors ; 2, in the canines, and 

 3, in the molars ; and of each of these I hope to give one or 

 two well-marked examples. 



We find in the incisor series specialisation of either the 

 central or lateral incisors, either in one or both jaws, by 

 unusual lengthening or by absence in a functional condition, 

 altogether of one or both, or of all the incisors in one jaw, or 

 even by extreme lengthening of one single incisor on the one 

 side of the mouth. 



Thus in the Edentata, which comprise the sloths and 

 armadillos, whose teeth are what are called " Homodont," i.e., 

 similar in structure throughout the series, there being no 

 specialisation into canines, molars, &c., but are all of a simple 

 pattern, we find in some complete absence of front teeth, as in 

 the Mutica or " South- American Ant-eater," in which the 

 elongated jaws can hardly open at all, the mouth being a 

 small slit at the end of the elongated muzzle ; or the Manis or 

 " Scaly Ant-eater," and none of the order possess central 

 incisors. 



This peculiarity is in keeping with the creatures' mode of 

 life. Their food being ants and other insects, they procure 

 their prey by protruding an enormously long tongue, which is 

 covered with viscid saliva, to which the insects stick, and by 

 the retraction of the tongue are brought within the bite of 

 the back teeth by which they are masticated. 



Amongst the Cetacea, whose teeth are also of the 



