Snake Skin

Function and Morphology

Reptile skin functions to protect from physical trauma, desiccation, infection, osmotic damage and extremes of temperature. There are several layers. The dermis is mainly connective tissue but contains the pigment cells. The epidermis is characterised by scales that are covered with keratin. The size and shape of scales varies greatly among species: the bushmaster has scales that are large with a dermal core or osteoderm while they may be partially overlapping and keeled in the rattlesnake. The smallest scales are seen in the boids and worm snakes. The ventral scales (or scutes) are generally larger and thicker than the lateral and dorsal scales.

The skin of reptiles has numerous functions including display, protection, camouflage, thermoregulation and fluid homeostasis.

The skin is dry, with few glands compared with mammals and amphibians.

Epidermis

The epidermis consists of 3 layers:

• Stratum germinativum - which divides and produces keratin.
• Stratum intermedium - which contains lipid, thus preventing fluid loss.
• Stratum corneum - which forms scales and scutes.

In reptiles, 2 forms of keratin are present:

• Alpha-keratin which is flexible and often found between scales and scutes and in hinges.
• Beta-keratin which is unique to reptiles. It is harder than alpha-keratin and forms scutes and scales.

Dermis

The dermis of reptiles contains pigment cells, nerves and vessels, although thick, keratinised skin is without cutaneous sensation, leaving captive reptiles at risk of thermal burns.

• Find out more about snake vesicular dermatitis (blister disease).

Scales

There is much variation in the size and shape of scales among species of snakes. For instance the bushmaster has scales that are large with a dermal core or osteoderm while they may be partially overlapping and keeled in the rattlesnake. The smallest scales are seen in the boids and worm snakes.

Glands

Almost no skin glands occur in snakes, but coacal scent glands (anal glands) are present. They occur at the base of the tail, dorsal to the hemipenes in a male, and open into the posterior margin of the cloaca. These organs play a role in defense resulting from their unpleasant odour, which may also carry social signals. These may become enlarged, impacted, or abscessed in captivity.

Skin adaptations and cutaneous appendages

• Spectacles - are clear scales over the eyes of snakes.
• Heat sensory pits (infrared-sensitive receptors) - are deep grooves between the nares and the eye of pit vipers, pythons and some boas which allow them to 'see' the radiated heat of their prey. These pits can also be found on the upper lip, just below the nares, termed 'labial pits'.
• Rattle - present in some snakes and used to warn predators. It is enlarged with each shed.
• Gastrosteges - are a single row of large ventral scales in snakes that aid locomotion.

References

Mader, D.R. (2005). Reptile Medicine and Surgery. Saunders. pp. 51 ISBN 072169327X