Dorsal scales

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Dorsal scales on a banded krait, Bungarus fasciatus. AB 053 Banded Krait.JPG
Dorsal scales on a banded krait, Bungarus fasciatus.

In snakes, the dorsal scales are the longitudinal series of plates that encircle the body, but do not include the ventral scales. [1]

Snake wiggling animal without legs

Snakes are elongated, legless, carnivorous reptiles of the suborder Serpentes. Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws. To accommodate their narrow bodies, snakes' paired organs appear one in front of the other instead of side by side, and most have only one functional lung. Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca. Lizards have evolved elongate bodies without limbs or with greatly reduced limbs about twenty-five times independently via convergent evolution, leading to many lineages of legless lizards. Legless lizards resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule is not universal.

Ventral scales

In snakes, the ventral scales or gastrosteges are the enlarged and transversely elongated scales that extend down the underside of the body from the neck to the anal scale. When counting them, the first is the anteriormost ventral scale that contacts the paraventral (lowermost) row of dorsal scales on either side. The anal scale is not counted.

When counting dorsal scales, numbers are often given for three points along the body, for example 19:21:17. These numbers correspond to the number of dorsal scales around the body at a head's length behind the head, at midbody and at a head's length before the vent. If only one number is given, it is for the midbody count. [1]

Dorsal scale are easiest to count diagonally, starting with the paraventral scale row. [1] In doing so, it is often noted that certain scale rows are raised, keeled or smooth as opposed to the others. [2]

Paraventral scales

In snakes, the paraventral scales are the longitudinal rows of dorsal scales that contact the ventral scales. These are the first rows of dorsal scales on either side of the body and are usually slightly larger than the scales located more dorsally. In species that have mostly keeled scales, the paraventrals are usually smooth or only weakly keeled.

Keeled scales

Keeled scales refer to reptile scales that, rather than being smooth, have a ridge down the center that may or may not extend to the tip of the scale, making them rough to the touch. According to Street's (1979) description of European lizards and snakes, in those that have keeled scales the keels are usually stronger in male specimens and are consistently arranged according to the species of reptiles, even though many others do not have them. With European lizards, the dorsal scales are usually well keeled, while those on the flanks are more weakly keeled and those on the belly smooth.

See also

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References

  1. 1 2 3 Campbell JA, Lamar WW (2004). The Venomous Reptiles of the Western Hemisphere. Ithaca and London: Comstock Publishing Associates. 2 volumes. 870 pp. 1,500 plates. ISBN   0-8014-4141-2.
  2. ↑ U.S. Navy (1991). Poisonous Snakes of the World. United States Government. New York: Dover Publications Inc. 203 pp. ISBN   0-486-26629-X.


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