Final answer:
The conjunctiva, while not part of the eye's three-layered structure, consists of two parts, the palpebral and bulbar conjunctiva, and includes layers like the epithelium with goblet cells and the underlying stroma with connective tissues.
Step-by-step explanation:
Anatomy of the Eye
The conjunctiva is a mucous membrane that covers the front of the eye and lines the inside of the eyelids. It is not part of the three-layer structure of the eyeball which is composed of the fibrous tunic, vascular tunic, and neural tunic. The conjunctiva itself is typically divided into two parts: the palpebral conjunctiva, which is attached to the inner surface of the eyelids, and the bulbar conjunctiva, which covers the anterior surface of the sclera but not the cornea.
The layers of the conjunctiva include the epithelium and the underlying stroma or substantia propria. The epithelium is a non-keratinized, stratified columnar epithelium that contains goblet cells, which are responsible for secreting mucin to lubricate the eye. Beneath the epithelium, the stroma consists of loose connective tissue that contains blood vessels, nerves, and immune cells. In contrast, the three layers of the eye's wall are the fibrous tunic, including the sclera and the cornea, the vascular tunic or uvea, comprising the iris, ciliary body, and choroid, and finally, the neural tunic, which contains the retina with its associated cells and synaptic layers.