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Snake (reptile), common name for any reptile belonging to the suborder Serpentes. The body is greatly elongated and most often cylindrical, but the sea snakes and many tree-dwelling snakes have bodies that are flattened laterally. Snakes lack external limbs, although a few still retain tiny remnants of hind legs, the tips of which are visible in large boas and pythons at the base of the tail. |
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| The body is covered with scales of
a horny epidermal material, arranged in regular rows and usually overlapping,
like tiles on a roof. The scales located on the back and sides are characteristically
smaller than those on the top of the head and along the ventral (under)
surface. The scales on the dorsal (upper) surface of the snake may be
smooth or may bear a long raised ridge or keel; other scale modifications
may include small knobs and tiny pits. The skin and outer covering of
the horny scales are shed periodically and usually in one piece, including
the hard, transparent covering of the eye known as the spectacle; snakes
lack movable eyelids, and the spectacle protects the constantly open eyes.
The frequency of shedding varies with different species and within a species,
according to the size and age of the individual. Young, rapidly growing
snakes shed their skins more frequently than the slow-growing adults.
In some species the skin is shed approximately every 20 days; in others
it is shed only once a year.
Venom is a complex mixture of proteins that destroy various tissues of the body, immobilizing or killing the prey. Venoms are frequently classified in two major categories: neurotoxic, or nerve-affecting, and haemotoxic, or blood-affecting. Actually all venoms contain elements of both types, but one type usually predominates. In general, the neurotoxic type is more effective, usually acting on the central nervous system to produce respiratory failure or suppression of the heart action. Haemotoxins destroy blood cells, the lining of the blood vessels, and other tissue. Because of the local destruction of circulatory cells, haemotoxic venoms spread more slowly and have a slower action than the neurotoxins. Snakes are found in all the warmer parts of the world, except on a number of oceanic islands. They occur as far north as the Arctic Circle in Europe, but the number of varieties decreases rapidly from the Tropics towards the poles. About 2,500 different species are known. They are classified in eight to ten families, depending on the system of classification employed for some of the specialized burrowing snakes and arboreal (tree-dwelling) snakes. The family Colubridae is the largest and includes the most common snakes found on all continents except Australia. It includes many harmless snakes such as the garter snakes and the rat snakes. |
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In Australia snakes of the Elapidae family outnumber
all others. It includes some of the deadliest snakes in the world, such
as the mambas, cobras, and coral snakes. Two other important groups
of venomous snakes are the pit vipers, including the rattlesnakes, the
bushmaster, and the fer-de-lance, of the family Crotalidae, and the
true vipers, including the adders, of the family Viperidae, into which
both groups are sometimes placed. The largest snakes in the world are
members of the family Boidae, which includes the boas and pythons. Some
members of this family never attain a length of more than 0.6 m (2 ft);
the giants of the family occasionally reach a size of more than 9 m
(30 ft). "Snake (reptile)," Microsoft(R) Encarta(R) 97 Encyclopedia. (c) 1993-1996 Microsoft Corporation. All rights reserved. |
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