Snake dentition
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Although most snake species are harmless to humans, several lineages have evolved venom with which to subdue their prey. This venom is typically delivered via specialized teeth ("fangs") located on the maxilla, a bone in the upper jaw.
[edit] General snake dentition
In most snakes, there are teeth on the dentary of the lower jaw (front-most jaw bone), the maxilla (outer front upper jaw bone), and the palatine and pterygoid, which form an 'inner row' of teeth. This 'inner row' can move separately from the rest of the jaws, and is used to help 'walk' the jaws over the prey. Some snakes, particularly burrowing snakes, have lost some or all of the teeth on various bones (in some cases only retaining a few lower or upper teeth)), but most snakes will have at least some teeth on each of the bones listed.
[edit] Categories
Most snakes can be placed into one of four groups, based on their teeth. The form of their teeth strongly correlates with venom and evolutionary lineage.
Aglyphous ("lacking grooves") snakes have no specialized teeth - each tooth is more or less the same in shape and often in size. When some teeth are larger than others, as is sometimes the case in bird eaters such as Corralus, the enlarged teeth are merely "scaled up", and are otherwise identical. Aglyphous snakes are non-venomous, and can be found in numerous families.
Opisthoglyphous ("rearward grooves") snakes are similar to aglyphous snakes, but possess weak venom, which is injected by means of a pair of enlarged teeth at the back of the maxillae. These "fangs" typically point backwards rather than straight down, possess a groove which channels venom into the prey, and are located roughly halfway back in the mouth, which has led to the vernacular name of "rear-fanged snakes". This combination of features means that, in order to envenomate prey, the snake must bite it, move the prey into the back of the mouth, then penetrate it with the grooved fangs, which allow venom secreted into the mouth to seep into the prey. This presents difficulties with large prey items, though they can quickly move smaller prey (or a human handler's finger) into position. While the venom of most opisthoglyphous snakes is so weak that it does not affect humans, a few are capable of delivering harmful or even fatal bites. Notably, herpetologists Karl Schmidtt and Mertens were killed by a boomslang and theletornis, respectively, after each underestimated the effects of the bite and failed to seek medical help. Opisthoglyphous snakes are found in family Colubridae.
Proteroglyphous ("forward grooved") snakes have a much more sophisticated venom delivery method. These snakes have shortened their maxillae, which bears few teeth except for a substantially enlarged "fang" located at the front of the mouth. Unlike the opisthoglyphous snakes, the fangs of proteroglyphs point downwards and completely fold around the venom channel, forming a hollow needle with which to inject their venom more effectively. However, because the fangs are only a fraction of an inch long in even the largest species (and often much shorter) these snakes must still hang on, at least momentarily, as they inject the venom. The venom of proteroglyphs is the most toxic of all snakes, and among the most toxic natural substances in the world. This form of dentition is unique to elapids. A few species of spitting cobras have modified the opening at the tip of the fang to allow them to spray venom at an attacker's eyes.
Solenoglyphous ("pipe grooved") snakes have the most advanced venom delivery method of any snake, unique to the vipers. Their maxillae have been reduced to mere nubs which support only a single hollow fang on each, which can be half the length of the head (almost 2 inches long in large species). The fangs are typically "folded back" against the roof of the mouth, pointing backwards, to accommodate their great length. During a bite, the fangs swing forwards into position. While all snake jaws have numerous interconnections between the bones, the viper skull have been modified into a series of interacting elements which cause the fangs to swing into biting position as a direct result of the jaws opening. Vipers open their mouths almost 180 degrees, and the fangs swing into a position to allow them to penetrate deep into the prey. While viper venom is typically less toxic than that of elapids, this system allows them to inject large quantities of venom deep into the prey animal.
[edit] Others
A few snakes do not conform to these categories. Attractaspis possess swinging fangs like a viper, but the fangs swing out sideways, allowing the snake to strike without opening its mouth, presumably to kill prey in small tunnels underground. The blind burrowing snakes (scolecophidia) typically have few teeth, often only in the upper jaw or lower jaw.