Is transparent and allows light into eye.
Contains smooth muscle fibres and encircles the opening or pupil.
Regulates the light passing through to the retina
Is an odd vascular choroid body thought to nourish the retina and control pH.
Is a depression in the retina that contains a high concentration of cone cells.
Provide additional gas exchange surfaces.
Hold air only during an inhalation.
Hold air only during an exhalation.
Hold air during both inhalation and exhalation.
Do nothing. The air sacs have no physiological function.