SKELETAL TISSUES -

1. These connective tissues form the endoskeleton of the vertebrates.
2. These support the body, protect the various organs and help in locomotion.
3. Skeletal tissues include cartilage and bone.

CARTILAGE -

1. Cartilage is a soft skeletal tissue.
2. It is not rigid like bone.
3. It is found more abundantly in vertebrate embryoes because most of the bones forming skeleton of the adult are cartilaginous in the early stage.
4. The cartilages are of three types.

(a) Hyaline cartilage

1. It contains clear, large amount of translucent, slightly elastic matrix with less fibres.
2. The matrix often has very fine white fibres which are difficult to observe.
3. It forms articular surfaces at the joints of long bones, where it is called articular cartilage.
4. It also forms part of larynx and sternum, rings of trachea and bronchi, sternal parts of ribs, hyoid apparatus and nasal cartilages.
5. Most of the embryonic skeleton consists of hyaline cartilage.
6. Hyaline cartilage forms the skeleton of elasmobranch fishes and the embryonic skeleton in bony vertebrates.

(b) Fibrous cartilage -

1. It has well developed fibres in the matrix.
2. It is of two types -

(i)  White Fibrous Cartilage or White Fibrocartilage -

1. The matrix is firm and has abundant white fibres.
2. It occurs in the intervertebral discs where it acts as cushion and in the pubic symphysis where it helps in parturition.
3. White fibrous cartilage is the strongest cartilage. (ii) Yellow Elastic Fibrocartilage -
4. The matrix contains numerous yellow fibres.
5. Due to the presence or yellow fibres, the cartilage becomes more flexible.
6. This type of cartilage is found in the pinna and external auditory canal of the ear, Eustachian tubes, epiglottis and tip of the nose. It makes these organs flexible.

(c) Calcified cartilage -

1. Sometimes matrix contains granules of calcium crabonate, then the cartilage is called calcified cartilage.
2. Calcium carbonate makes the cartilage hard and inelastic.
3. This cartilage is found in suprascapula of pectoral girdle of frog and vertebrae of shark.