INTRODUCTION

• The hard parts of an animal body present inside or outside the body collectively form the skeletal system.
•  Skeleton serves as the reservoir of many minerals, like calcium and phosphate.
•  The marrow of the long bones is the site for the haemopoiesis, i.e., formation of blood cells (RBC, WBC, plallets).
•  The skeleton plays a vital role in movement and locomotion.
•   Human skeleton consists of 206 pieces of bones.
•   In infants 306 bones are present.

•     Girdle bones: These provide a connection between the axial skeleton and limbs. The two girdles are nam ed as pectoral and pelvic girdles, respectively.

                                                        JOINTS

    Joints are the place of articulation between two or more bones or between a bone and a cartilage. Due to the presence of a number of joints, the movement of the
   different body parts and the whole body is possible.
    Types of Joints :
    (i) Fixed or immovable or fibrous joint: There is no space between the bones. The attached bones are tightly held with the help of white fibrous connective tissue.
    e.g., Joints of skull bones.
    (ii) Slightly movable or cartilaginous joint: It is an articulation between the bones that allows very little movement. e.g., Between bones of vertebrae and pelvic girdle.
    (iii) Movable joint or synovial joint: It is a joint which allows the movement of articulating bones such that they can move extensively upon each other. The space between
           bones is called synovial cavity. This cavity remains filled with a viscous and slippery synovial fluid. These are of following types :
    (A)     Ball & socket joint : One bone forms a ball like head that fits into a socket formed in the other bone. The bone with head can move nearly in all the
          directions. e.g. Shoulder JOint, hip joint.
    (B)    Hinge joint : This joint allows movements in one plane only. e.g. Elbow joint & knee joint.
    (C)    Pivot joint: This joint allows only a rotatory movement of one bone on the other stationary bone. e.g. Atlas and axis vertebrae.
    (D)    Angular joint I Ellipsoid I CondylOid joint - This allows movement in two directions -side to side and back & forth . e.g. Wrist joint.