In snake

Snake

Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...

s, the dorsal scales are the longitudinal series of plates that encircle the body, but do not include the ventral scales

Ventral scales

In snakes, the ventral scales 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 row of dorsal scales on either side...

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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.

Dorsal scale are easiest to count diagonally, starting with the paraventral scale row

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 doing so, it is often noted that certain scale rows are raised, 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...

or smooth as opposed to the others.