What bones make up the shoulder girdle in the upper appendicular skeleton?

The shoulder girdle, also known as the pectoral girdle, is primarily composed of two bones: the scapula and the clavicle. The scapula, or shoulder blade, is a flat bone that provides a broad surface for muscle attachment and helps to connect the upper limb to the trunk. The clavicle, commonly referred to as the collarbone, serves as a strut that stabilizes the shoulder and connects the arm to the body.

These two bones work together to form a flexible and mobile structure that allows for a wide range of motion in the upper limb. This mobility is crucial for activities such as reaching, lifting, and throwing. The shoulder girdle also serves as an attachment point for multiple muscles that control the movement of the shoulder and arm, reinforcing its importance in upper body function.

The other options listed involve bones that are part of different regions of the skeleton. The humerus and radius are part of the arm, while the ulna and phalanges are associated with the forearm and fingers, respectively. The carpals and metacarpals pertain to the wrist and hand. Hence, only the scapula and clavicle correctly identify the bones that constitute the shoulder girdle in the upper appendicular skeleton.