Welcome to Zoology World

balindrakumar033@gmail.com   25/11/2017,Saturday



What is osteology

The study of bone structure and treatment of bone disorders is called osteology.

Skeleton is the hardest tissue
of the body


The hardened tissue of the body together form the skeleton (sclero=hard).Skeleton of invertebrates is most often secreted on the surface, forming a lifeless or dead exoskeleton.Whereas skeleton of vertebrates develops most often underneath the surface forming a living or growing endoskeleton.Three types of skeletons develop in vertebrate

1.Epidermal/Horney exoskeleton

These include hard and horny keratinized derivatives of epidermal layer of skin ,such as claw, most reptilian's scales,bird feathers and mammalian hairs, horns nails and hoof etc.All living amphibians lack an exoskeleton.

2. Dermal/Bony skeleton

Dermal bony skeleton is derived from the dermis of skin.It includes bony scales and plates or scutes(osteoderms),finrays and antlers of fishes, some reptiles(crocodiles,turtles and tortoises) and mammals.In fishes ,dermal scales become exposed due to wearing out of epidermis,and form exoskeleton.


Greater part of vertebrate skeleton lies more deeply,forming the endoskeleton .It develops from mesenchyme.Endoskeleton is formed by bones in vertebrates.Skeleton


Having no skeleton i.e; porifera,coelenterata, helminth,Annelida.

b. Vertebrates

In vertebrates dermal skeleton is formed by bone.Bone is the connective tissuewith intercellular spaces filled with ossein matrix composed of 25% water,25% protein fibres,50% mineral salts.The inner most region is full of bone marrow having various types of cells .In mammals the bone is full of haversian canals.

The bone are of following type:-

(i) cartilage bone:-

The bones which are formed by the ossification of preexiting cartilage are called cartilage bone or replacing bone.e.g., vertebra, Girdles, limb bones, basioccipital, supraoccipital, sphenoid, Incus, malleus, .

(ii)Membrane or dermal bones

The bones which are formed by independent ossification in connective tissue are called dermal,membrane or investing bone e.g., Ribs, Sternum ,clavicle, Nasal, vomer, palatine,maxilla.

(iii) Sesamoid bones:-

Ossification takes place on ligament e.g.,cotyloid bone of Rabbit and tendons e.g., Patella, Pisiform.

(vi) Pneumatic bones:-

Bones with hollow spaces containing air e.g.,bones of birds , frontal,sphenoid,ethmoid maxilla of human.

(v) Irregular bones:-

Vertebrae are irregular bone.

(vi) Flat bones:-

Cranial bone,scapula ,ribs

(vii) Short bones:-

Carpals and tarsals.

Functions of endoskeleton:-

Chief function of vertebrate endoskeleton can be enumerated as follows:-

(i) To provide physical support to body by forming a firm and rigid internal framework.

(ii) To give definite body shape and form.

(iii)To protect delicate internal organs like brain,lungs

(iv) To permit growth of huge body size(whale,elephant,extinct dinosaurs),since it is living and growing.

(v) To provide surface for attachment of muscles.

(vi) To serve as levers on which muscles can act.

(vii) To help in breathing(tracheal rings,).

Skeleton is the hardest tissue
of the body

Endoskeleton of vertebrates