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Explain the structure of epidermal scales.
horny, tough extensions of the stratum corneum
periodically molted or shed gradually along with the rest of the stratum corneum
Organisms that have epidermal scales
well developed in reptiles; also common on exposed skin in birds (confined to lower legs, feet, base of bill) and mammals
absent in fish
clawlike epidermal scales are present in certain amphibians; horns of hte horned lizard are specialized epidermal scales
these scales cover the bony scales of the carapace and plastron of turtle shells
Composition of cosmoid scales
enamel,. dentine (cosmine) vaxular and lamellar bone), thinner, and have dentine of cosmoid type
cycloid or rhomboid
Thick, rhomboid, evolved from cosmoid scales.
Ganoin,vascular bone and lamellar bone
Derived from ganoid scale of lepidosteoid type.
• Scales thin, imbricated, and cycloid or ctenoid
Placoid scales (dermal denticles)
Evolved from cosmoid scales?
Lack the bony basal layer of scales.
• Pulp cavity surrounded by dentine--this capped with enamel.