Preheat oven to 225 degrees F (110 degrees C). Line 2 baking sheets with aluminum foil and grease the foil.
Beat egg whites with cream of tartar and salt in a bowl with an electric mixer until egg whites are foamy. Gradually beat in sugar, a few tablespoons at a time, beating until the sugar dissolves in the meringue before adding more. Continue beating until the meringue is glossy and forms a sharp peak when beaters are lifted straight up out of the bowl; beat in vanilla extract. Spoon the meringue into a pastry bag fitted with a small tip.
Pipe meringue into small bone shapes on the prepared aluminum foil. You must pipe all the shapes at once or the meringue will deflate.
Place cookie sheets into the preheated oven and bake for 1 hour. No not open oven door or peek during baking. Turn the oven off and let the meringue bones cool in the oven without opening door for 1 hour. Gently and carefully remove cookies from aluminum to prevent broken bones.
