AUSTRALIAN SNAKES. 11 



most lizards have the ear fully ex[)Osecl. Snakes can 

 withdraw their long forked tongues wholly within a 

 sheath situated in the floor of the mouth, and liere we 

 liave such a feature as we seek, for there is no such 

 sheath in lizards, the tongue being attached in the 

 more usual manner. In all lizards the two bones 

 forming the lower jaw are firmly united in front, 

 whereas in snakes the nnion is an elastic substance 

 which allows the bones to be widely separated ; the 

 bones of the upper jaw are in certain snakes also 

 distensible, and the junction of the lower jaw with the 

 skull is not so direct, the quadrate bone being specially 

 developed and having much more play than in lizards. 

 The object of these cranial peculiarities is to enable a 

 snake to swallow a larger animal than would otherwise 

 ^nter the mouth, for mastication, properly so-called, is 

 not performed. Speaking of bony characters, it may 

 be mentioned that there are an enormous number of 

 vertebrae, or separate bones, in the spinal column, and 

 that each is provided with a ball at one end and a cup 

 at the other, into which the ball of the preceding 

 vertebra exactly fits ; the snake is thus enabled to twist 

 and turn itself about without fear of dislocating its spine. 



The scales which cover the body are not true scales, 

 that is, they are not separate structures like, say, the 

 scales of a fish, and cannot be plucked out. The outer 

 skin is thrown into regular folds or pleats, and the 

 exposed portions are provided with horny plates. 



