460 THE ANTIQUITY OF MAN 
V-shaped gap between the crown of the lower canine and 
the first milk molar, rubbing against the outer surface of 
these two lower teeth in exactly the same manner as in 
an ape. There is this difference, however : while the 
canine of the ape wears in such a way as to maintain 
a sharp chisel edge, the points of the human canines 
become rubbed away. To explain the pointed conical 
form and the manner in which the human milk canine 
teeth come into opposition, we must suppose that they 
were used at one time as in anthropoids. The develop- 
mental history of the human permanent canines also 
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Fig. 170. — Skull of a child, dissected to show the roots of the milk teeth and the 
crowns of the permanent canines in process of development. 
requires explanation. The budding crowns of the 
permanent teeth are situated at the roots of the milk 
teeth which they are destined to replace — all except the 
canine teeth. The crown of the upper canine, as in the 
anthropoid, begins to form far above the other members 
of the series — under the roof of the orbit (fig. 170). 
The lower canine appears near the lower border of the 
mandible. A deep origin for the canine is a necessity in 
an anthropoid. The longer the root of a tooth, the 
deeper in the jaw must the crown of the tooth be 
developed ; the tip of the root is the last part of a tooth 
to form, and it is formed at the spot where the crown 
