The correct answer is option 'D': Scapula and clavicle.

The pectoral girdle, also known as the shoulder girdle, is the skeletal framework that connects the upper limbs (arms) to the axial skeleton. It consists of two main bones: the scapula (shoulder blade) and the clavicle (collarbone). Let's discuss these bones in more detail:

Scapula:
The scapula is a large, flat triangular bone located on the back of the shoulder. It is commonly referred to as the shoulder blade. The scapula has several important features, including:

1. Spine: The spine of the scapula is a prominent ridge that runs diagonally across the posterior surface of the bone. It serves as an attachment site for muscles and ligaments.

2. Acromion process: The acromion process is a bony projection that extends from the top of the scapula. It forms the outer edge of the shoulder and articulates with the clavicle.

3. Glenoid cavity: The glenoid cavity is a shallow, socket-like structure on the lateral aspect of the scapula. It is the point of articulation with the head of the humerus, forming the shoulder joint.

Clavicle:
The clavicle is a long, S-shaped bone that connects the sternum (breastbone) to the scapula. It is positioned horizontally above the first rib and acts as a strut between the arm and the axial skeleton. The clavicle has several important landmarks, including:

1. Sternal end: The sternal end of the clavicle is the medial (closer to the midline of the body) portion that articulates with the sternum.

2. Acromial end: The acromial end of the clavicle is the lateral (further from the midline of the body) portion that articulates with the acromion process of the scapula.

Functions of the Pectoral Girdle:
The pectoral girdle serves several important functions, including:

1. Support: It provides support and stability to the upper limbs, allowing for the wide range of motion of the arms.

2. Muscle attachment: The pectoral girdle serves as an attachment site for various muscles that move the arms and shoulders.

3. Protection: It helps protect vital structures, such as the brachial plexus (nerves) and blood vessels that pass through the shoulder region.

In conclusion, the pectoral girdle is constituted by the scapula and clavicle. These bones provide support, stability, and mobility to the upper limbs, allowing for various arm and shoulder movements.