The pectoral girdle, also known as the shoulder girdle, is an anatomical structure that connects the upper limbs (arms) to the axial skeleton. It consists of several bones, including the clavicle (collarbone) and the scapula (shoulder blade). The pectoral girdle provides stability and mobility to the upper limbs, allowing for various movements of the arms.

a. Sternum:

- The sternum, also known as the breastbone, is a flat bone located in the middle of the chest. While it is not directly part of the pectoral girdle, it plays an important role in connecting the clavicles to the axial skeleton.
- The clavicles articulate with the sternum at the sternoclavicular joints, forming one of the connections between the upper limbs and the axial skeleton.

b. Acetabulum:

- The acetabulum is a cup-shaped socket located on the lateral side of the pelvis. It is part of the hip bone or innominate bone, which consists of the ilium, ischium, and pubis.
- The acetabulum is not part of the pectoral girdle. Instead, it forms the socket where the head of the femur (thigh bone) articulates, forming the hip joint.

c. Glenoid cavity:

- The glenoid cavity, also known as the glenoid fossa, is a shallow depression located on the lateral side of the scapula. It forms part of the shoulder joint, where the head of the humerus (upper arm bone) articulates.
- The glenoid cavity is an integral part of the pectoral girdle, as it provides a connection point for the upper limb and allows for the wide range of movements of the shoulder joint.

d. Ilium:

- The ilium is one of the three bones that make up the hip bone or innominate bone. It forms the upper and largest part of the pelvis.
- While the ilium is not directly part of the pectoral girdle, it is important for understanding the overall structure of the body. The ilium contributes to the stability of the pelvis and provides attachment sites for various muscles, including some that contribute to the movements of the upper limbs.

In summary, the pectoral girdle consists of the clavicle and scapula, while the sternum indirectly connects to it. The acetabulum and ilium are not part of the pectoral girdle but are important components of the pelvis and hip joint. The glenoid cavity, located on the scapula, is a key part of the pectoral girdle as it contributes to the shoulder joint and upper limb movements.

Glenoid cavity