Final answer:
The free edge of the nail primarily serves to protect the tip of the finger or toe. It is composed of keratin-filled epidermal cells that form a hard, protective plate.
Step-by-step explanation:
The primary purpose of the free edge of the nail is to protect the tip of the finger or toe. Nails, including the free edge, are made of specialized epidermal cells filled with keratin, making them tough and hard. This is essential for their role in forming protective plates over the digit tips. Additionally, they provide a counterforce to the sensitive fingertips when handling objects, which enhances sensory perception. The free edge, or free margin, being the part that extends beyond the digit, is particularly involved in this protective function.