Dermis of Animals


The second layer of the skin that lies below the epidermis is called the dermis. Dermis includes blood vessels, small nerves, and pigment cells. It also contains lymphatics, sensory receptors, the basis of multicellular glands, hairs or feathers, and their erector muscles.

The main component of the dermis is collagenous connective tissue. Collagen is a proteinaceous fibril which aggregates with other collagen fibers to form a dense bundle of collagenous connective tissue.

Dermis in Amphioxus

The dermis is of different nature in amphioxus. It mainly consists of a layer of gelatinous material having few fibers except in its inner and outer borders.

Dermis in Fishes


In fishes, the dermis has evolved the ability to form dermal scales or plates. In fishes, dermal scales or plates are classified as:

  1. Cosmoid scales
  2. Ganoid scales
  3. Placoid scales
  4. Modern bony scales
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Cosmoid scales:

They were present on early lobe-finned fishes and are not found in any fish today alive. They are precursors of ganoid, placoid, and modern bony scales. A substance called cosmine was present in the dentin of these scales. That is why called Cosmoid scales.

Ganoid scales:

There are two types of ganoid scales. The first type is called, paleoniscoid scales which are genuine, old-fashioned ganoid scales present on Polypterus, Latimeria, and Calamoichthyes. The second type known as lepidosteoid scales is present on garfish. They have no dentin or ganoid.

Placoid scales:

They are present on sharks, rays, and skates and show resemblance to the denticles of ostracoderms which were ancient armored fishes. In this type of scale, dentin and enamel formed a spine that protrudes through the typical epidermis.

The basal plate embedded in the dermis is thin lamellar bone. These scales change into teeth at the margin of jaws.

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Modern bony scales:

There are two types of modern bony scales.

  1. Cycloid scales
  2. Ctenoid scales

They are the characteristic of teleosts and modern lobed-finned fishes. The only difference between the two types is that ctenoid scales have a comb-like free border called Ctenoid.

Fishes such as Cyclostomes, eels, and catfishes have lost the ability to form scales.

Dermal Ossification in tetrapod

In tetrapods, bony dermal scales are called osteoderms. Osteoderms develop on some amphibians, reptiles, and few mammals. Birds lack any dermal scales.


Apodans – the limbless amphibians and some tropical toads have dermal scales. In the osteoderms are microscopic between the furrows of skin and macroscopic within furrows.


They have large oval osteoderms. The young of some species of lizards have osteoderms under the epidermal scales of the head. Except for leather backs, turtles are truly armored vertebrates.


Among mammals, dermal armor is present only in Armadillos and t lies below the dermal scales.

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Function of dermis
  • Maintain body temperature (thermoregulation).
  • Aid in controlling blood pressure and flow.
  • Has sensory receptors so respond to pressure, heat, cold, etc.
  • Support the skin.
  • Protect the deeper layers of skin.