Identification of cephalic scales is most conveniently begun with reference to the nostril, which is easily identified on a snake. There are two scales enclosing the nostril which are called the nasals. In colubrids, the nostril lies between the nasals, while in vipers it lies in the centre of a single nasal scale. [22] The outer nasal (near the snout) is called the prenasal while the inner nasal (near the eye) is called the postnasal. Along the top of the snout connecting the nasals on both sides of the head are scales called internasals. Between the two prenasals is a scale at the tip of the snout called the rostral scale. [22]

Tsuji, L.A.; Müller, J. (2009). "Assembling the History of the Parareptilia: Phylogeny, diversification, and a new definition of the clade". Fossil Record. 12 (1): 71–81. Bibcode: 2009FossR..12...71T. doi: 10.1002/mmng.200800011. a b Piñeiro, Graciela; Ferigolo, Jorge; Ramos, Alejandro; Laurin, Michel (2012). "Cranial morphology of the Early Permian mesosaurid Mesosaurus tenuidens and the evolution of the lower temporal fenestration reassessed". Comptes Rendus Palevol. 11 (5): 379–391. Bibcode: 2012CRPal..11..379P. doi: 10.1016/j.crpv.2012.02.001.a b Sander, P. Martin (2012). "Reproduction in early amniotes". Science. 337 (6096): 806–808. Bibcode: 2012Sci...337..806S. doi: 10.1126/science.1224301. PMID 22904001. S2CID 7041966. Hansen, D.M.; Donlan, C.J.; Griffiths, C.J.; Campbell, K.J. (April 2010). "Ecological history and latent conservation potential: Large and giant tortoises as a model for taxon substitutions". Ecography. 33 (2): 272–284. doi: 10.1111/j.1600-0587.2010.06305.x.

Euryapsida– one high fenestra (above the postorbital and squamosal)– protorosaurs (small, early lizard-like reptiles) and the marine sauropterygians and ichthyosaurs, the latter called Parapsida in Osborn's work. Molnar, Ralph E. (2004). Dragons in the Dust: The paleobiology of the giant monitor lizard Megalania. Bloomington: Indiana University Press. ISBN 978-0-253-34374-1.

International

Directorate General Armed Forces Medical Services, India. Memorandum No 102: Snakebite. Undated.pdf available [ online]. Accessed on 21 Feb 2010. As mentioned previously, the most dominant form of reptile reproduction is oviparous or egg-laying reproduction, but there are a few notable exceptions. Around 20% of all lizards and snakes, including the boas, do produce live young instead of eggs. These viviparous reptiles have a non-mammalian placenta or some other means through which nutrients are transferred from the mother to the offspring and vice versa for the waste. The main advantage of viviparous birth is that it protects the eggs from predators in a hostile environment. But this method of birth has a tradeoff, since it’s taxing on the mother.

Tsuji, Linda A. & Müller, Johannes (2009). "Assembling the history of the Parareptilia: phylogeny, diversification, and a new definition of the clade". Fossil Record. 12 (1): 71–81. Bibcode: 2009FossR..12...71T. doi: 10.1002/mmng.200800011. a b Thorpe, Roger S.; Thorpe, R. S.;Wüster, Wolfgang & Malhotra, Anita (1997). Venomous snakes: ecology, evolution, and snakebite. Vol. 70 of Symposia of the Zoological Society of London. Oxford University Press, London. ISBN 0-19-854986-5. Scale arrangements are important, not only for taxonomic utility, but also for forensic reasons and conservation of snake species. [19] Excluding the head, snakes have imbricate scales, overlapping like the tiles on a roof. [20] Snakes have rows of scales along the whole or part of their length and also many other specialised scales, either singly or in pairs, occurring on the head and other regions of the body.Hearing in humans relies on 3parts of the ear; the outer ear that directs sound waves into the ear canal, the middle ear that transmits incoming sound waves to the inner ear, and the inner ear that helps in hearing and keeping your balance. Unlike humans and other mammals, snakes do not possess an outer ear, a middle ear, and a tympanum but have an inner ear structure with cochleas directly connected to their jawbone. [93] They are able to feel the vibrations generated from the sound waves in their jaw as they move on the ground. This is done by the use of mechanoreceptors, sensory nerves that run along the body of snakes directing the vibrations along the spinal nerves to the brain. Snakes have a sensitive auditory perception and can tell which direction sound being made is coming from so that they can sense the presence of prey or predator but it is still unclear how sensitive snakes are to sound waves traveling through the air. [94] Skin [ edit ] Skin of a sand lizard, showing squamate reptiles iconic scales Russell, Anthony P.; Bauer, Aaron M. (2020). "Vocalization by extant nonavian reptiles: A synthetic overview of phonation and the vocal apparatus". The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology. 304 (7): 1478–1528. doi: 10.1002/ar.24553. PMID 33099849. S2CID 225069598. The origin of the reptiles lies about 310–320 million years ago, in the steaming swamps of the late Carboniferous period, when the first reptiles evolved from advanced reptiliomorphs. [33] [ failed verification] Farmer, C.G. (2000). "Parental care: The key to understanding endothermy and other convergent features in birds and mammals". American Naturalist. 155 (3): 326–334. doi: 10.1086/303323. PMID 10718729. S2CID 17932602. Phylogenetic classifications group the traditional "mammal-like reptiles", like this Varanodon, with other synapsids, not with extant reptiles