Snakes have often been associated with evil, either for cultural reasons or, directly, because of our survival instinct. We fear and respect them and the venom they use to hunt and defend themselves. However, as it usually happens, fear is diluted when our knowledge about them increases. In fact, they are not all equally poisonous and dangerous. It depends on the location in the upper jaw, structure and presence or not of their fangs. Thus, we can distinguish 4 types of snakes:
The prefix already tells us everything: these snakes do not have fangs to inject venom or inoculation ducts. It is the most primitive condition and its best known representatives are anacondas and boas.
They already have venom fangs, but they are located in the posterior part of the jaw, far back, and small ducts through which the venom will flow. Due to their location, it is difficult for them to sink their fangs, so they are not usually dangerous. E.g.: bastard snake (Malpolon monspessulanus).
The fangs are already in a more advanced position, in the premaxillary, and are dangerous. Cobras and mambas, for example, are proteroglyphous, so there is little more to say. Some species of cobras have a modification that allows them to drop the venom in their mouth and then blow it out strongly and spit it out.
Here we have the vipers and rattlesnakes. They have the most specialized and effective venom apparatus. They have two pairs of fangs on each side, arranged in the anterior part of the mouth and perforated. The venom ducts runs through them, which ensures its inoculation after opening a wound with the fangs.
Did you know that snakes have more teeth in addition to the venom fangs? In this regard, they are homodonts (all teeth are the same, unlike ours) and polyphiodonts (they undergo several dental replacements).