32 ELEPHANTS. 



and tusks, a larger surface for the attachment of the muscles 

 which support the head is necessary, and even in the small 

 Eocene Moeritherium change in this direction had begun. 



In the fossil mammals it is the teeth that are of the greatest 

 importance in settling the relationships of different species to 

 one another, and in forming an opinion as to their food and 

 probable manner of life. 



The reason for the importance of fossil teeth is, that while in 

 many ways they are very conservative, long retaining traces of 

 the earlier forms from which they have originated, nevertheless 

 they readily undergo change in accordance with the kind of 

 food they are called upon to seize and masticate. Moreover, 

 from their hardness they are more frequently preserved than 

 most other parts of the skeleton. It will be well, therefore, 

 before considering the teeth of Moeritherium and the other 

 Proboscidea to give a short account of mammalian teeth in 

 general, so that the descriptions later may be understood. 

 Central The tooth of a mammal (see Mammalia in Index collection 

 T? al j in Central Hall) consists of a root or roots embedded in 

 a socket in the jaw, and a crown which is exposed and is 

 adapted for the work it has to perform. In a section of a tooth 

 (fig. 6) it is seen that the greater part is composed of a hard 

 material called dentine, and that the crown of the tooth is usually 

 covered with a still harder substance known as enamel, while 

 in some cases the root, and in others (usually the more com- 

 plicated forms) both root and crown, may be coated with a softer 

 bony matter, called cement. The form of the crown differs 

 enormously in different animals and in different parts of the 

 mouth : it may be a simple cone like the canine or dog-tooth, 

 or it may form a large complicated grinding surface as in the 

 back teeth of the horse. The teeth are usually divided into 

 different series according to their particular position in the 

 mouth and the duties they have to perform (see figs. 1 & 2). 

 The front teeth implanted in the anterior part of the jaw are 

 mainly concerned in grasping and biting off the food : these are 

 called incisors. In mammals which, like the pig (fig. 1), possess 

 the primitive number of teeth, there are three of these on either 

 side in both upper and lower jaws. Behind these come the 



