The =eye= or =organ of vision= (Organon visus) in the broader sense of
the term comprises the eyeball or globe of the eye, the optic nerve, and
certain accessory organs associated therewith. The accessory organs
(Organa oculi accessoria) are the orbital fasciæ and muscles, the
eyelids and conjunctiva, and the lacrimal apparatus. These structures
will be considered in the order in which they may be most conveniently
examined, taking the horse as a type. The bony walls of the orbit have
been described in connection with the skull; the periorbita, a fibrous
membrane which incloses the eyeball together with its muscles, vessels,
and nerves, may be appropriately included in the account of the fasciæ.
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