Which of the following is NOT part of the human skeleton?

The brain is not part of the human skeleton because it is a vital organ housed within the skull, which is categorized as part of the axial skeleton but does not constitute a bone itself. The human skeleton is primarily composed of bones that provide structure, support, and protection to the body, while the brain serves as the control center for the nervous system.

In contrast, the femur, humerus, and tibia are all bones that are integral components of the human skeleton. The femur is the thigh bone, the longest bone in the body, the humerus is the bone of the upper arm, and the tibia is one of the two bones in the lower leg, commonly referred to as the shin bone. Understanding the distinction between bone structure and organ composition is essential in anatomy, highlighting the role of each component in the overall system of the human body.