Which of the following structures is included in the axial skeleton?

The axial skeleton is a major part of the human skeleton that consists of bones along the body's long axis, primarily providing support and protection to the brain, spinal cord, and the organs of the thorax. This includes the skull, vertebral column, and rib cage.

The ribs are essential components of the axial skeleton as they form the rib cage, which safeguards vital internal organs such as the heart and lungs, while also playing a crucial role in the respiratory system. The structure and attachment of the ribs to the spine illustrate their importance in the axial alignment and function of the skeleton.

In contrast, the pelvis, radius, and scapula do not belong to the axial skeleton. The pelvis is part of the appendicular skeleton, which supports the limbs and facilitates their movement. Similarly, the radius and scapula are also classified under the appendicular skeleton, as they are involved in limb movement and connection rather than the axial support and structure.