Skeleton is therefore, the hard framework on which the body is built. This hard framework may be made up of sand particles as in Arcellar (a shelled Amoeba), exoskeleton as in insects and snails, cartilage as in the cartilaginous fish, bones and less cartilage in the bony fish and other vertebrates.
Functions of the skeleton
- Protection: It gives protection to the delicate organs of the body. For example, the skull protects the brain, eyes and ears. The thoracic bones protect the heart and lungs. The vertebral column protects the spinal cord.
- Support: The rigid framework of the skeleton gives support to the body. The cervical vertebrate support the head and the bones of the hind-limbs support the upper parts of the body.
- Muscle attachment: Skeleton provides places for the attachment of muscles.
- Movement: The movement of certain parts of the body is brought about by the bones when muscles act on him. The contraction and relaxation of the muscles of the legs bring about motion.
- Manufacture of white and red blood cells: The white and red blood cells are manufactured in the bone marrows of the long bones.
- Breathing: The thoracic bones aid breathing movement.
- Shape: Skeleton gives shape to the body.
- Transmission of sound waves: The three small, soft and light bones found in the middle ear (malleus or hammer, incus or anvil, stapes or stirrups) vibrate and transmit sound waves from the middle ear to the inner ear.
Types of skeleton
There are three types of skeleton found in animals and they are:
- Hydrostatic skeleton.
- Exoskeleton: Any hard structure which gives shape, and forms the framework of the body of the animals located externally on the animals constitutes the exoskeleton. The exoskeleton may cover the entire external surface of the of body such as in insects and many other arthropods where it protects the animals against dessication in the dry habitat, or serves as hydrofuge against wetting in aquatic habitat. The shells in the molluscs, tortoise and turtle are also of this type. Tortoise and turtle have both exoskeleton and endoskeleton.
- Hydrostatic skeleton: Hydrostatic skeleton is found in soft-bodied animals, such as earthworms and sea anemones. It consists of the body fluid secreted by the body wall and stored in the coelom. The fluid being inside a closed system presses against the muscles (longitudinal and circular) of the body wall. These muscles in turn contract against the fluid. Hydrostatic skeleton is thus constructed on the principles of the combined effects of fluid pressure and muscle contraction ina closed system to maintain the shape and form of the animal. It goes further to perform for the animals, the functions of support, protection and movement.
- Endoskeleton: All hard parts of the body found inside the body of the animals (in other words the skeleton that lies inside the body of the animals), on which all the soft parts are built is called endoskeleton. Endoskeleton is found in the vertebrates with very few occurrence in invertebrates such as the corals, (Coelenterata), sepla and octopus. Endoskeleton is made up largely of bone with little cartilage. In the cartilaginous fishes, the endoskeleton is made up entirely of cartilage without bone materials.