Which structure is not part of the skeleton?

The heart is not part of the skeleton. The skeletal system is made up of bones and cartilages that provide support, protect vital organs, and enable movement through the attachment of muscles. The heart, on the other hand, is a muscular organ responsible for pumping blood throughout the body. It plays a crucial role in the circulatory system but is not a part of the skeletal framework.

In contrast, the skull, sternum, and vertebrae are all integral components of the skeleton. The skull houses and protects the brain, the sternum serves as a central element in the ribcage, and the vertebrae together form the spine, providing structural support and protecting the spinal cord. Each of these structures fulfills essential functions related to the skeletal system, distinguishing them from the heart.