Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 71

In birds and certain reptiles, the lower eyelid is larger and more mobile than the upper eyelid. There are no feathers corresponding to eyelashes on the lids. The superciliary line refers to feathers that correspond to the eyebrow and are often of different colors than surrounding feathers. The superciliary or supraorbital ridge refers to the unfeathered bony protuberance just dorsal to the orbital rim that is seen in many raptors, such as eagles and hawks. The ridge is thought to provide shade to the eye. Birds may blink with both eyelids or the NM alone. In contrast to mammals, the thin nearly transparent NM of birds is under direct skeletal muscular control with two muscles extraneous to the lid that can pull the NM over the entire cornea as many as 15–20 times/min, even with the other eyelids closed. Blinks in peacocks are strongly associated with gaze shifts. The NM also contains a superficial tear gland, and some species have a deeper harderian gland. Chicks hatch with their eyes open.