A cavity known as glenoid cavity is present at the tip of scapula and coracoid. process, for artlculation of head of humerus. Pectoral girdle consists of a membranous bone called clavicle and a large replacing bone called shoulder blade or scapula coracoid.

Parts of Pectoral Girdle
- Glenoid Cavity: The glenoid cavity is a shallow socket on the scapula bone that articulates with the head of the humerus, forming the shoulder joint. It is a crucial part of the pectoral girdle as it allows for the free movement of the shoulder joint.
- Sternum: The sternum, also known as the breastbone, is a long flat bone located in the center of the chest. It serves as an attachment point for the ribs and plays a vital role in protecting the heart and lungs. While the sternum is part of the axial skeleton, it is not considered a component of the pectoral girdle.
- Ilium: The ilium is one of the three bones that make up the hip bone, along with the ischium and pubis. It is not a part of the pectoral girdle, as it is located in the pelvic region and is involved in supporting the weight of the body and connecting the lower limbs to the axial skeleton.
- Acetabulum: The acetabulum is a deep socket on the hip bone that articulates with the head of the femur, forming the hip joint. While the acetabulum is an important part of the pelvic girdle, it is not considered a component of the pectoral girdle.
Therefore, the correct answer is the Glenoid Cavity, which is a key part of the pectoral girdle as it plays a crucial role in shoulder joint movement and stability.