The master cylinder is connected to each wheel by brake lines and hoses. Brake hoses are specially constructed flexible tubes with metal ends for transmitting fluid under extreme pressure. The entire hydraulic system is filled with a special brake fluid, which is forced through the hoses by the movement of the master cylinder's pistons. If they appear cracked or brittle, the hoses should be replaced immediately. Close inspection of the brake hoses is a good way to prevent catastrophe!