Which structure of the eye is NOT included in the fibrous tunic?

The iris is the correct answer because it is part of the vascular tunic, not the fibrous tunic of the eye. The fibrous tunic consists of the sclera and cornea, which provide structural support and protection to the eye. The sclera is the white outer layer of the eyeball, while the cornea is the transparent front part that allows light to enter and begins the process of focusing that light.

In contrast, the iris is the colored part of the eye and controls the size of the pupil, thereby regulating the amount of light that enters the eye. It is made up of muscle fibers and connective tissue, and its primary function is related to the vascular system rather than providing structural support. Understanding these distinctions between the various tunics of the eye helps clarify the roles and relationships of these components within the ocular anatomy.