Exoskeleton Structure of mammals

General Structure

• The integument is one of the largest organs of the body. Making of somehow 15% of the human body weight.
• The skin is composed of an out of epidermis and inner-dermis.
• Between epidermis and dermis lies the basement membrane, consisting of basal lamina and reticular lamina.
• Epidermis is derived from the ectoderm and produces the basal lamina.
• Dermis develops from mesoderm and produces reticular lamina.
• Between the integument and deep body musculate is present is transitional subcutaneous region made of very connective and adipose tissue. This is known as hypodermis.

General structure of Mammalian Epidermis

• Epithelial cells of the epidermis are called Keratinocytes.
• The surface Keratinized cells are continuously exfoliated and replaced by cells arising primarily from the deepest layer of the epidermis called stratum basale.
• As the cells are displaced to higher levels they pass through keratinization stages exhibited as distinct successive layers towards the surface.
  
  1. Stratum spinosum
  2. Stratum granulosum
  3. Stratum lucidum
  4. Stratum corneum
• In addition to this epithelial cell type chromatophores became secondarily associated with the epidermis. They secret the granules of melanin which are eventually carried into the stratum corneum and into the shaft of hair.
• Skin colour results from a combination of yellowish stratum corneum, the red blood vessels and the dark pigment granules secreted by the chromatophore.

Structure Of hair

• Hairs are slender keratinous filaments.
• The base of hair is called the root.
• The remaining length of the hair constitutes the shaft.
• The outer surface of the shaft forms a scaly cuticle.
• Beneath the cuticle is the hair cortex and the core is called hair medulla.
• The shaft of the hair projects above the surface of the skin, but it is produced within an epidermal hair follicle routed in the dermis.
• At its expanded base the follicle receives a small tuft of the dermis called hair papillae.
• Chromatophores in the follicle contribute pigment granule to the hair shaft to give it colour.
• A thin band of smooth muscle called arrector pillar, anchored in the dermis, is attached to the follicle and makes the hair stands erect as response to cold, fear and anger.

Types of hair cover

• A thick covering of hair is called fur. It is composed of guard hairs and underfur.
• The guard hairs are longer coarse hair and are apparent on the outer surface of the fur.
• The underfur is present beneath the guard hairs and are usually much finer and shorter. Both guard hairs and underfur act as insulators.
• In most marine mammals underfurs are reduced or lost entirely and only a few guard hairs are present.
• In some cases sensitive nerves are associated with the roots of the vibrissae present around the mouth.
• The quills of porcupines are stiff coarse hairs modified for defense.

Claws, Hooves and Nails

• Claws, Hooves and Nails are modifications of the stratum Corneum at the end of the dease.
• They have the almost same basic structure.
• They are mostly made of 2 curved parts.
• A horni dorsal plate called engius and a soft ventral plate called subunguis.
• The 2 plates wrap partially around the terminal phalanx. [mammals phalangeal formula 2:3:3:3:3]
• Claws are curved laterally compressed keratinised projections from the tips of the digit. They are found in most birds, reptiles and mammals.
• Nails are plates of tightly compacted epithelial cells on the surface of the fingers and toes.
• They protect the tips of the digits from injury. Only primates have nails.
• Hooves are enlarged keratinised plates on the tips of the ungulate digits. The thick horny unguis of a hoove is ‘U’ and ‘V’ shaped and consists of dead cells. And soft callus like cornified pad, called counties, are frequently present in ungulates partially surrounded by the subunguis.
• Claws first appear in reptiles and have persisted in birds and most mammals. It involves nails in primate and into hooves in ungulates.

Horn

• Found in the members of the family Bovidae (Cow, sheep,goat, antelope, bison etc. )
• True horn consists of a core of dermal bone covered by a keratinised sheath.
• Horns occur in both males and females and are retained throughout the ear. They also continue to grow throughout life.
• They are unbranched except in pronghorn antelopes.

Antlers

• Antlers are found in the members of the family Corvidae(deer)
• Only males have antlers which are branched antlers and shed annually.
• Antlers when growing the bonycore is covered by a living skin called velvet. Which apparently shapes and provides vascular supply to the growing bone. Eventually the velvet falls away to unsheath the bare bone.
• In the caribou, bothsexes have seasonal antlers.

Hair horne

• They are not actually true hornes.
• They can be differentiated from other hornes by being composed of agglutinated keratinised hairlike epidermal fibres that form a solid horne.
• Hair horns remain partch on a roughened area of the nasal bone.
• Both sexes have hair horns, and they don't shed. Eg. Rhinoceros, Africa rhino’s have, one behind the other.
• The horns of giraffes resemble the stunted antlers. They are short, bony projections of the frontal bones that remain in velvet throughout the light.

Horn and Antler

Scales

The unfeather areas in the body of the birds such as tursus, metatarsus the four digits of the hindlimb and around the base of the beak are covered by overlapping epidermal scales. The scales are dry, wavy and arranged in an overlapping fashion.

Claws

In most birds the claw is confined to the toes. The claws have become variously modified depending upon the need.

• The cursorial(which can run first) and walking birds often bear long digits to provide a good base for balance.
• Aquatic birds have webbed feet for swimming.
• The Feet of the jungle fowl are modified for running and stretching the soil in search of food.
• In hawks, claws are recurved and the toes have rough raised pads to gross the prey.
• In wood-peackers, the claws are very much curved to help the feet to cling to the smooth vertical surface of the trees.

Beaks

These ar ehorny epidermal structures which cover the upper and lower jaws.The outer and parts of the horny covering are called rhamphotheca. The beak is used during ingestion of food, preening of feathers and fighting. Because of functional diversity and different food habits beaks exhibit a variety of forms.

• In egyptian vultures the beak is hooked and pointed to tear off flesh from the cercasses.
• In flaming gows the beak is provided with marginal hooks and forms a filtering mechanism through which is passed out.
• In Tundus sp. (American Robin) the beak is moderately long to enable it to feed on fruits.
• Birds that mainly eat seeds usually have short, thick, strongly built bills. Eg. Parrot.