Definition: External ear (pinna) length is a standard measurement in mammalogy, usually measured in a living mammal or a fresh mammal carcass. External ear length is measured from the base of the notch at the bottom of the ear to the apex (highest point) of the ear.
Definition: Because of the difference in refractive index between air and water (or corneal tissue), a curved cornea is an image-forming lens in its own right. Its focal length is determined by the radius of curvature of the cornea. Many corneal eyes (eg: in land vertebrates) also have lenses, but the lens is flattened and weakened compared with an aquatic lens; most of the refractive power is provided by the cornea. Corneal eyes cannot focus in aquatic habitat.