Which of the following is NOT a part of epithelial tissue?

Epithelial tissue plays a critical role in covering and protecting the surfaces of the body, both internally and externally. It forms the outer layer of the skin, lines various body cavities, and makes up the mucous membranes that protect and lubricate surfaces. The skin serves as a prime example of epithelial tissue, providing protection against environmental damage. Mucous membranes, also composed of epithelial cells, line various passages in the body, including the oral cavity and respiratory tract, providing a barrier and facilitating secretions.

The lining of the heart, known as the endocardium, is another instance of epithelial tissue. This layer is crucial for the functioning of the heart as it provides a smooth surface for the blood to flow and helps to protect the underlying muscle tissue.

In contrast, bone is classified as connective tissue rather than epithelial tissue. Bone has a distinct function, structure, and composition, serving to support and protect the body's structure and facilitate movement through its connection with muscles. Given its primary role in structure and support, bone does not share the properties or functions associated with epithelial tissue. Therefore, it accurately represents the correct answer to the question, as it does not belong to the category of epithelial tissue.