a substance secreted in a glandular sac under the skin of the abdomen of the male musk deer, having a strong odor, and used in perfumery. 2. an artificial imitation of the substance. 3. a similar secretion of other animals, as the civet, muskrat, and otter. 4. the odor of musk or some similar odor.
Lens: The lens is a clear part of the eye behind the iris that helps to focus light, or an image, on the retina. Macula: The macula is the small, sensitive area of the retina that gives central. vision. It is located in the center of the retina. Optic nerve: The optic nerve is the largest sensory nerve of the eye. It. carries impulses for sight from the retina to the brain. Pupil: The pupil is the opening at the center of the iris. The iris adjusts the size. of the pupil and controls the amount of light that can enter the eye.
The Eye. Vision begins at the eye, where light rays are focused onto light-sensitive elements at the back of the eye. The main parts of the eye are: The cornea -- the transparent front of the eyeball. The cornea acts as a lens and in fact is responsible for most of the bending of the light rays needed to focus an image at the back of the eye.