Snake scale

The scales of a snake primarily serve to reduce friction as it moves, since friction is the major source of energy loss in snake locomotion. s get their name from the coloration of their scales caused by iridescence. The ventral (or belly) scales, which are large and oblong, are especially low-friction, and some arboreal species can use the edges to grip branches. Snake skin and scales help retain moisture in the animal's body. Snakes pick up vibrations from both the air and the ground, and can differentiate the two, using a complex system of internal resonances (perhaps involving the scales). ==Evolution==

Reptiles evolved from amphibious ancestors which left the water and became terrestrial. To prevent loss of moisture, reptilian skin lost the softness and moisture of amphibian skin and developed a thick stratum corneum with multiple layers of lipids, which served as an impermeable barrier, as well as providing protection from ultraviolet light. Over time, reptilian skin cells became highly keratinised, horny, sturdy and desiccated. The surfaces of the dermis and epidermis of all reptilian scales form a single contiguous sheet, as can be seen when the snake sheds its skin as a whole. ==Morphology==

'', a colubrid.|alt=Section of body of a snake is shown. It has brown, black and buff coloured scales. The vretebral scales form a buff-coloured row in which the keels are prominently seen. Snake scales are formed by the differentiation of the snake's underlying skin or epidermis. Each scale has an outer surface and an inner surface. The skin from the inner surface hinges back and forms a free area which overlaps the base of the next scale which emerges below this scale. Snakes have smaller scales around the mouth and sides of the body which allow expansion so that a snake can consume prey of much larger width than itself. Snake scales are made of keratin, the same material that hair and fingernails are made of. Surface and shape Snake scales are of different shapes and sizes. Snake scales may be granular, have a smooth surface or have a longitudinal ridge or keel on it. Often, snake scales have pits, tubercles and other fine structures which may be visible to the naked eye or under a microscope. Snake scales may be modified to form fringes, as in the case of the eyelash bush viper, Atheris ceratophora, or rattles as in the case of the rattlesnakes of North America. long and pointed with pointed tips, as in the case of the green vine snake Ahaetulla nasuta, broad and leaf-like, as in the case of green pit vipers Trimeresurus spp. At birth, a rattlesnake hatchling has only a small button or 'primordial rattle' which is firmly attached to the tip of the tail. A new section is added each time the skin is shed until a rattle is formed. The rattle grows as the snake ages but segments are also prone to breaking off and hence the length of a rattle is not a reliable indicator of the age of a snake. Colour Scales mostly consist of hard beta keratins which are basically transparent. The colours of the scale are due to pigments in the inner layers of the skin and not due to the scale material itself. Scales are hued for all colours in this manner except for blue and green. Blue is caused by the ultrastructure of the scales. By itself, such a scale surface diffracts light and gives a blue hue, while, in combination with yellow from the inner skin it gives a beautiful iridescent green. Some snakes have the ability to change the hue of their scales slowly. This is typically seen in cases where the snake becomes lighter or darker with change in season. In some cases, this change may take place between day and night. Snake scales are not discrete but extensions of the epidermis hence they are not shed separately, but are ejected as a complete contiguous outer layer of skin during each moult, akin to a sock being turned inside out. Moulting is repeated periodically throughout a snake's life. Before a moult, the snake stops eating and often hides or moves to a safe place. Just before shedding, the skin becomes dull and dry looking and the eyes become cloudy or blue-colored. The inner surface of the old outer skin liquefies. This causes the old outer skin to separate from the new inner skin. After a few days, the eyes clear and the snake "crawls" out of its old skin. The old skin breaks near the mouth and the snake wriggles out aided by rubbing against rough surfaces. In many cases the cast skin peels backward over the body from head to tail, in one piece like an old sock. A new, larger, and brighter layer of skin has formed underneath. An older snake may shed its skin only once or twice a year, but a younger, still-growing snake, may shed up to four times a year. The discarded skin gives a perfect imprint of the scale pattern and it is usually possible to identify the snake if this discard is reasonably complete and intact. ==Arrangement==

Scale arrangements are important, not only for taxonomic utility, but also for forensic reasons and conservation of snake species. Excluding the head, snakes have imbricate scales, overlapping like the tiles on a roof. 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. The dorsal (or body) scales on the snake's body are arranged in rows along the length of their bodies. Adjacent rows are diagonally offset from each other. Most snakes have an odd number of rows across the body though certain species have an even number of rows e.g. Zaocys spp. The maximum number of rows are in mid-body and they reduce in count towards the head and on the tail. ==Nomenclature==

The various scales on a snake's head and body are indicated in the following paragraphs with annotated photographs of Buff-striped Keelback Amphiesma stolata, a common grass-snake of South Asia and a member of Colubridae, the largest snake family. Head 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. 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. The circumorbital scales towards the snout or the front are called preocular scales, those towards the rear are called postocular scales, and those towards the upper or dorsal side are called supraocular scales. Circumorbital scales towards the ventral or lower side, if any, are called subocular scales. Between the preocular and the postnasal scales are one or two scales called loreal scales. or abdominal scales (scutes, plates). Many authors simply abbreviate the ventral scales as "V". The number of ventral scales can be a guide to the species. Details of scales of Buff-striped Keelback have been taken from Daniels. ==Glossary==

from Malcolm A. Smith (1943). • Scales on the head • Rostral • Nasorostral • Nasal • Prenasal • Postnasal • Supranasal • Fronto-nasal • Internasal • Brille, spectacle, ocular scale, eyecap • Circumorbital • Preocular • Postocular • Supraocular • Subocular • Loreal • Interorbital, intersupraocular • Frontal • Prefrontal • Parietal • Occipital • Interoccipital • Temporal • Labial • Supralabial, upper labial • Sublabial, infralabial, lower labial • Mental or symphysial • Chin shield • Anterior chin shield, anterior genials • Posterior chin shield, posterior genials • Intergeneial • Gular • Scales on the body • Dorsal • Vertebral • Ventral, gastrostege • Scales on the tail • Cloacal • Subcaudal, urostege Other terms • Canthus, or canthus rostralis – the angle between the supraocular scale and the rostral scale • Mental groove ==Taxonomic importance==

Scales do not play an important role in distinguishing between the families but are important at generic and specific level. There is an elaborate scheme of nomenclature of scales. Scales patterns, by way of scale surface or texture, pattern and colouration and the division of the anal plate, in combination with other morphological characteristics, are the principal means of classifying snakes down to species level. In other places with large biodiversity, such as Myanmar, publications caution that venomous and non-venomous snakes cannot be easily distinguished apart without careful examination. The scales patterning may also be used for individual identification in field studies. Clipping of specific scales, such as the subcaudals, to mark individual snakes is a popular approach to population estimation by mark and recapture techniques. Distinguishing between venomous and non-venomous snakes ''), an Elapid, with no loreal scale between nasal and pre-ocular scales.|alt=The head of a snake facing to the left pinched between thumbs. The gape is open and tongue protuding. The dorsal scales are coloured black and the ventral scales are yellowish-white in colour. The scales on the head are prominently seen as are the nostril and black beady eye between which are two hexagonal scales. There is no simple way of differentiating a venomous snake from a non-venomous one merely by using a scale character. Finding out whether a snake is venomous or not is correctly done by identification of the species of a snake with the help of experts, or in their absence, close examination of the snake and using authoritative references on the snakes of the particular geographical region to identify it. Scale patterns help to indicate the species and from the references, it can be verified if the snake species is known to be venomous or not. Species identification using scales requires a fair degree of knowledge about snakes, their taxonomy, snake-scale nomenclature as well as familiarity with and access to scientific literature. Distinguishing by using scale diagrams whether a snake is venomous or not in the field cannot be done in the case of uncaught specimens. It is not advisable to catch a snake to check whether it is venomous or not using scale diagrams. In certain regions, presence or absence of certain scales may be a quick way to distinguish non-venomous and venomous snakes, but used with care and knowledge of exceptions. For example, in Myanmar, the presence or absence of loreal scales can be used to distinguish between relatively harmless Colubrids and lethally venomous Elapids. ==Cultural significance==

, Arizona.|alt=Five pairs of cowboy boots in a row facing half-right, all having snake-skin uppers. The first three pairs have uppers of gray and tan scales and ankle pieces of ecru colour. The last two pairs have uppers with prominent black and white diamond shaped scale patterns and navy blue ankles. Snakes have been a motif in human culture and religion and an object of dread and fascination all over the world. The vivid patterns of snake scales, such as the Gaboon Viper, both repel and fascinate the human mind. Such patterns have inspired dread and awe in humans from pre-historic times and these can be seen in the art prevalent to those times. Studies of fear imagery and psychological arousal indicate that snake scales are a vital component of snake imagery. Snake scales also appear to have affected Islamic art in the form of tessellated mosaic patterns which show great similarity to snake-scale patterns. The use of snakeskin has however endangered snake populations and resulted in international restrictions in trade of certain snake species and populations in the form of CITES provisions. Animal lovers in many countries now promote the use of artificial snakeskin instead, which are easily produced from embossed leather, patterned fabric, plastics and other materials. A snake scale was portrayed as a clue in the 1982 film Blade Runner. Snake scales also figure in popular fiction, such as the Harry Potter series (desiccated Boomslang skin is used as a raw material for concocting the Polyjuice potion), and also in teen fiction. ==See also==