216 NEW ZEALAND NATURE-STUDY BOOK 
The eyes are large and prominent, and placed on the 
sides of its head. In this position they are able to com- 
mand a wide range of view. 
Mouth and teeth. Rabbits are much given to gnaw- 
ing young trees, being fond of the bark and _ soft tissue 
underneath. Tame Rabbits indulge their gnawing propen- 
sities by rasping away the wood of the hutch—though 
this can be of no use as food. ‘The front of the palate is 
hard and rough, on the tongue is a hard pad, and on the 
inside of each cheek is a horny patch covered with hair ; 
these protect the cheeks from splinters of wood and other 
hard substances which find their way into the mouth. 
The gnawing is done with the sharp front teeth called 
incisors, which project from the middle of the upper and 
lower jaw. ‘These are four in number, two in each jaw, 
and are long and curved with exceedingly sharp cutting 
edges. <A split or cleft in the upper lip enables the two 
upper incisors to be seen even when the mouth is closed. 
The cleft allows the upper teeth freer play, and enables the 
lip to be drawn aside, and so escape being injured during 
the process of gnawing. 
The hardest part of the tooth, a substance called enamel, 
is at the front, and forms the cutting edge. Behind the 
enamel is a mass of dentine, which grows softer towards the 
inside of the tooth. This difference of composition results 
during the process of gnawing in the inner surface being 
most worn away, and the outer surface least—and thus a 
sharp chisel-edge is maintained. The teeth of rodents 
moreover grow constantly from the bottom, so that the 
upper surfaces when worn away are immediately replaced. 
Directly behind the two incisors of the upper jaw, is 
another and smaller pair, which can easily be felt by the 
finger. The enamel faces of these are directed backwards, 
so that the softer portions of the two sets of upper incisors 
