Fill in the Blanks Nail CompositionOnline version Take this quick quiz to see if you remember what you read. by Rosalind Carter 1 rigid 15 flexible 25 firm onyx integumentary keratin The natural nail is part of the system . The is the hard protective plate composed mostly of . A normal healthy nail is but . The water content of a nail is between and percent . The lower the water content , the more the nail .