The eyes comprise (a) the eye-ball or globe and (b) its appendages. The appendages comprise: 1. The Eyebrows which are arched eminences surrounded by hairs, situated over each orbit. 2. The Eye-lids (upper and lower)— are two movable folds, their inner and outer meeting points being called the internal and external canthii. In the inner canthus there is a fold of conjunctiva, called plica semilunaris. Opposite this, on the margin of each eye-lid is the lachrymal papilla, which is pierced by the punctum lachrymale, or the opening of the lachrymal canal. The lachrymal gland is situated in the upper angle of the orbit (the orbit has been described along with skull bones). It has a dozen ducts which open by apertures placed in a row at the inner surface of the upper lid. The lachrymal canal commences at the puncta lachrymalia and passes inwards to open into the lachrymal sac.
The eye-ball or globe is situated inside the orbit. It consists of
- Sclera—in the posterior part
- Cornea—in the anterior part
- Choroid—in the posterior part
- Iris—in the front part
- Two chambers
- Three Refractive media
- Aqueous Humor—in anterior chamber
- Crystalline Lens-on partition wall
- Vitreous Humor—in posterior chamber
It is kept in place by the Optic Nerve, which originates from base of brain and piercing the eye-ball from behind expands inside it as the retina. The eye is moved by a set of muscles situated on its outer surface, but inside the orbit. The cornea is its anterior transparent part. The Iris is the coloured membrane suspended in the aqueous humor in front of the lens.