The lower lid is the larger and often incloses a small cartilaginous plate. The _conjunctiva_ is a true mucous membrane which covers the anterior portion of the eye cavity attaching to the cornea-scleral juncture. The =choroidea= is rich in pigment. On its inner surface lies the dark pigment layer of the retina. The corpus ciliare, that part of the choroid coat bearing the ciliary processes, consist of numerous folds. The ciliary muscles are arranged obliquely. Each consists of three digitations. The _iris_ is covered on the posterior side with pigment, the color of which determines the color of the eye. The yellow pigment of the iris has been said to be due to carotin and xanthophyll and the black pigment to melanin. The enlarging and the contracting of the pupil is brought about by muscles. The reduction of the pupillary caliber is due to the sphincter pupillary muscle. It is said by some anatomists that the muscles controlling the caliber of the pupil in the bird furnish voluntary motion and that the capability of accommodation of the eyes is greater in birds than in mammals. The =retina= contains no blood-vessels; otherwise the structure is similar to that of mammals. The crystalline lens is flattened on the corneal side and is convex posteriorly. The lens epithelium develops into fibers in the parts close to the equator, and are almost perpendicular to the eye axis. The corneal portion is relatively small. The =sclerotic coat= is dense and white. It is divided into three layers. It is thin and flexible, and somewhat elastic posteriorly. It has an internal layer of hyaline cartilage. Anteriorly its form is maintained by the circle of osseous plates mentioned above. These plates, interposed between the exterior and the middle layer, are located immediately behind the cornea. The scales are thin and of oblong quadrate shape, being elongated from before backward. The choroid coat is a membrane loosely cellular and highly vascular. It is impregnated by a black pigment. Opposite the bony circle the choroid separates into two layers. The external layer is the thinner and adheres at first firmly to the sclerotic; it passes forward to become continuous with the iris. The inner layer is thicker than the external. The two layers are made up of radiating fibers which terminate anteriorly in the ciliary processes, the ends of which are adherent to the capsule of the crystalline lens. The iris is delicate in structure. It is composed of a fine network of interlacing fibers. The ciliary nerves and blood-vessels run in the form of single trunks between the choroid and the sclerotic, and terminate anteriorly in a ring-shaped plexus for the supply of the iris and the muscular circle of the cornea. As stated before, the pupil in the fowl is round, but in the goose it is elongate transversely; and in the owl, a vertical oval.