Introduction 
Next we have tuberculate teeth, with a flat crown from 
which arise rounded or pointed tubercles; such are many molars 
and premolars. Besides these there are the flat-topped teeth of 
horses, cows, elephants and many mice with tortuous ridges 
across their surface, these being the most complicated teeth known. 
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Sections of Teeth. 
1 An incisor or tusk of Elephant, with open pulp cavity at base. 2 Humar. 
molar with broad crown and two roots. 3 Molar of Ox, showing deeply folded enamel 
surface with cement filling up the depressions. (After LyDEKKER). 
A tooth grows from a soft “pulp” and in its early stage 
is open at the base, the cavity being occupied by the pulp. 
Some teeth remain this way and continue to grow on_ indefi- 
nitely while they wear away more or less at their tips. Such 
are the tusks of elephants and the incisor teeth of rats and other 
gnawing animals. Other teeth, on the contrary, gradually close 
up at the base, forming one or more roots or fangs, the rem- 
nant of the pulp being contained in the inside of the tooth. Such 
teeth do not increase in growth after the roots are formed. 
The substances that make up teeth are three: (1) dentine 
or ivory which forms the bulk of the tooth, (2) enamel, a very 
hard bluish-white substance which covers the outer surface, 
and (3) cement, a bone-like substance which fills up the cavities 
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