The fibroustunic is divided into the cornea, which is the transparent, exposed membrane in front of the lens, and the sclera, the firm, white coat of the eye to which is attached the muscles that move the eyeball.
Each half of the split beam travels down one arm and is reflected back by the mirror at the end of each arm.
The adult human eye is a hollow globe with a diameter of approximately 2.5 cm (1 in).