*The nostrils of the bird, which lead into the [[Nasal cavity - Anatomy & Physiology|nasal cavity]], may have a flap of horn to protect them, known as the ''Operculum''. | *The nostrils of the bird, which lead into the [[Nasal cavity - Anatomy & Physiology|nasal cavity]], may have a flap of horn to protect them, known as the ''Operculum''. |