Pectoral and Pelvic Girdles

In humans , the pectoral girdle holds the upper limbs or arms to the axial skeleton. It consist mainly of four separate bones : two large flat regular shoulder blades or scapulae (singular : scapula) at the  back and two slender collar bones or clavicles in front. The scapulae are attached to the vertebral column by muscles. each scapula has a depression called the glenoid cavity into which the head of the upper arm bone or humerus fits to form the shoulder joint. The clavicles are attached to a scapula at one end and to the sternum at the other end. The pectoral girdle is not rigid, enabling the arms and shoulders to move fairly , freely.

       In an adult human, the pelvic girdle or hips consists of two bones , the right and left pelvis. These are joined to the sacrum at the facets in front, to form a complete, rigid girdle. On the other edge of each pelvis is a deep cavity, the acetabulum, into which the head of the thigh bone or femur fits to form the hip joint. The pelvic girdle is designed to receive the weight of the upper body and pass it  on the legs ( if you are standing) or to the surface on which you are sitting. The rigid structure of the girdle restricts the movements of the hips and legs.