188 Life and Immortality. 
snakes, however, it is stored up in sacs, modifications of the 
salivary glands, and placed in each side of the upper jaw. 
From the poison-gland under the eye forward to the edge of 
the jaw, a delicate canal, which opens into the fang above the 
tube of the tooth, extends. Alongside of the latter may be 
seen rudimentary fangs, all ready to, grow out should the 
large one be lost. To use the poison, the snake has merely 
to strike its prey, when the muscles of the jaw, which are 
admirably fitted for the part they have to play in the tragedy, 
press upon the glands, squeeze the poison through the little 
canal down through the hollow fang, and the work is ac- 
complished. 
In their actions, snakes are most graceful. The gliding 
motion, so characteristic, is effected by the movements of 
the large central scales, that are successively pushed for- 
ward, the hinder edges resting on the ground and consti- 
tuting a support. These scales, or pushers, are fastened to 
the ribs by muscles, and by holding a snake by the hand the 
swelling movement can readily be felt. 
Snakes vary much in color. They are generally adapted 
to their surroundings. Green Snakes are found in green 
grass and vegetation, while grey snakes affect rocky dis- 
tricts, where they are alike protected. Their skin is shed in 
one piece at various seasons of the year, being forced off by 
the snake forming a ring with its tail and squeezing the rest 
of the body through it, or by wriggling through entangled 
bushes. Poisonous snakes may be always recognized by 
their broad, flattened heads, generally short and thick bodies, 
and the almost invariable possession of a vertical keel along 
the centre of each scale. Long bodies, small heads devoid 
of distinct necks, and scales not keeled, characterize non- 
poisonous species. 
Probably the best-known of our common kinds of poison- 
ous snakes are the rattlesnakes. They belong to the dan- 
gerous family Crotalide, to which the copperheads and 
moccasins also belong, and are distinguished by the large, 
