Editing Snake skeleton (section)

===Snake dentition===
In most [[snake]]s, [[tooth|teeth]] are located on the [[dentary]] of the [[lower jaw]], the [[maxilla]], the [[palatine bone]] and the [[lateral pterygoid plate]]. The latter form an "inner row" of teeth that can move separately from the rest of the jaws and are used to help "walk" the jaws over prey.  Several snake lineages have evolved [[snake venom|venom]] which is typically delivered by specialized teeth called [[fang]]s located on the [[maxilla]].

Most snakes can be placed into one of four groups, based on their teeth, which correlate strongly with venom and lineage.

====Aglyph====
[[Image:Python skull.jpg|thumb|left|An '''aglyphous''' snake. A [[Burmese python]] skull (''[[Python bivittatus]]'')]]'''Aglyphous''' snakes (''lacking grooves'') have no specialized teeth; each tooth is similar in shape and often size.  When teeth vary in size, as in some bird eaters, they do not vary in shape.  Most aglyphous snakes are non-venomous; some, like ''[[Garter snake|Thamnophis]]'', are considered mildly venomous. The feature is not a [[synapomorphy]].{{clear}}

====Opisthoglyph====
[[Image:Heterodon nasicus skull.jpg|thumb|left|An '''opisthoglyphous''' snake. A [[hognose snake]] skull (''[[Heterodon nasicus]]'')]]'''Opisthoglyphous''' ("rearward grooves") snakes possess venom injected by a pair of enlarged teeth at the back of the [[maxillae]], which normally angle backward and are grooved to channel venom into the puncture. Since these fangs are not located at the front of the mouth, this arrangement is [[Vernacular|vernacularly]] called "rear-fanged".  In order to envenomate prey, an opisthoglyphous snake must move the prey into the rear of its mouth and then penetrate it with its fangs, presenting difficulties with large prey although they can quickly move smaller prey into position. The opisthoglyphous dentition appears at least two times in the history of snakes.<ref>Bruna Azara, C. (1995). "''Animales venenosos. Vertebrados terrestres venenosos peligrosos para el ser humano en España'' ". ''Bol. SEA'' '''11''': 32-40.</ref> The venom of some opisthoglyphous snakes is strong enough to harm humans; notably, [[herpetologist]]s [[Karl Patterson Schmidt|Karl Schmidt]] and [[Robert Mertens]] were killed by a [[boomslang]] and a [[twig snake]], respectively,<ref>As herpetologists, both kept a record of the effect up to their death, Schmidt for a couple of days: https://people.wku.edu/charles.smith/chronob/SCHM1890.htm</ref><ref>Mertens kept a diary of his dying for full 18 days: cf Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). ''The Eponym Dictionary of Reptiles''. Baltimore: Johns Hopkins University Press. xiiiISBN 978-1-4214-0135-5. ("Mertens", p. 176; "Robert", p. 223; "Robert Mertens", p. 223).</ref> after each underestimated the effects of the bite and failed to seek medical help. Opisthoglyphous snakes are found mostly in the families [[Colubridae]] and [[Homalopsidae]]. {{clear}}

====Proteroglyph====
[[Image:Ophiophagus hannah skull.jpg|thumb|left|A '''proteroglyphous''' snake. A [[king cobra]] skull (''[[Ophiophagus hannah]]'')]]'''Proteroglyphous''' snakes (''forward grooved'') have shortened maxillae bearing few teeth except for a substantially enlarged fang pointing downwards and completely folded around the venom channel, forming a hollow needle. Because the fangs are only a fraction of an inch long in even the largest species, these snakes must hang on, at least momentarily, as they inject their venom.<ref>[http://seanthomas.net/oldsite/ld50tot.html LD50 for various snakes]</ref> Some [[spitting cobra]]s have modified fang tips allowing them to spray venom at an attacker's eyes. This form of dentition is unique to [[elapids]]. {{clear}}

====Solenoglyph====
[[Image:Crotalus skull.jpg|thumb|left|A '''solenoglyphous''' snake. A [[rattlesnake]] skull (''[[Crotalus]] sp.'')]]'''Solenoglyphous''' snakes (''pipe grooved'') have the most advanced venom delivery method of any snake. Each maxilla is reduced to a nub supporting a single hollow fang tooth. The fangs, which can be as long as half the length of the head, are folded against the roof of the mouth, pointing posteriorly.  The skull has a series of interacting elements that ensure that the fangs rotate into biting position when the jaws open.  Solenoglyphous snakes open their mouths almost 180 degrees, and the fangs swing into a position to allow them to penetrate deep into the prey.  While solenoglyph venom is typically less toxic than that of [[Snake skeleton#Proteroglyph|proteroglyph]]s, this system allows them to deeply inject large quantities of venom. This form of dentition is unique to [[Viperidae|viper]]s. {{clear}}

====Exceptions====
A few snakes do not conform to these categories.  ''[[Atractaspis]]'' is solenoglyphous but the fangs swing out sideways, allowing it to strike without opening its mouth, perhaps allowing it to hunt in small tunnels. [[Scolecophidia]] (blind burrowing snakes) typically have few teeth, often only in the upper or lower jaw.

====Informal or popular terminology====
Common names for the various types of snake dentition originate largely from older literature, but still are encountered in informal publications. Aglyphous snakes are commonly called '''fangless'''; opisthoglyphous snakes '''rear-fanged''' or '''back-fanged'''; and both proteroglyphous and solenoglyphous snakes are referred to as '''front-fanged'''.<ref name="Wrose">Rose, Walter; The reptiles and amphibians of southern Africa; Pub: Maskew Miller, 1950</ref><ref>Engelmann, Wolf-Eberhard.  Snakes (No. 05352). Publisher Bookthrift  1982. {{ISBN|978-0896731103}}</ref>