Then we have a clue, for each blade of whalebone grows from a horny white gum, being fed by a fleshy substance below much in the same way as our nails are, so that these blades are, as it were, a series of hardened ridges, which grow out from the soft palate, till they become frayed at the edges, and form that dense fringe which is the whale’s strainer, upon which he depends entirely for his food. Explain it as we will, however, it is a most wonderful apparatus. Imagine a huge upper jaw forming an arch more than nine feet high, so that if the whalebone were cleared away a man could walk about inside, upon the thick tongue which lies in the lower jaw fastened down almost to the tip so that it cannot be put out of the mouth. And then remember that this enormous mouth has to be filled with food sufficient to nourish a body fifty or more feet long. Who would ever guess that this food is made up of creatures so small that countless millions must go to a mouthful? Yet the whole difficulty is solved simply by these triangular fringed plates or mouth-ridges (see section Fig. 84, p. 318), covered with horny matter and frayed into minute threads like the horny barbs of a feather. Nor are we yet at the end of the wonderful adaptation, for while the jaw is only from nine to twelve feet high, the long outside edge of the plates is often eighteen feet long, and for this reason, that if they were only as long as the jaw is deep, then when the whale went fishing with his mouth open the animals would escape below the fringe, while as they now are, he may gape as wide as he will, the long curtain will still guard the passage of the mouth and entangle the prey in its meshes. But what, then, is to become of this great length of whalebone when the animal shuts his mouth? Here comes in the use of the beautiful elasticity of the plates, for the great Arctic whaler, Captain Gray, has shown that as the mouth shuts the lower ends of the longer plates bend back towards the throat and fall into the hollow formed by the short blades behind them, so that the whole lies compactly fitted in, ready to spring open again, and fill the gap whenever the jaws are distended. With this magnificent fishing-net the whalebone whales go a-fishing in all the salt waters of the world. They are not all of enormous size,--many of them are not more than twenty feet long,--nor have they all such a perfect mouthful of whalebone as the great Polar Whale; but when the whalebone is shorter, as in the Rorqual, and other whales with back fins, the stiff walls of the lower lip close in the sides of the mouth and prevent the escape of the prey; and many of these whales have a curious arrangement of skin folds under the lower jaw, which stretch out and enable them to take in enormous mouthfuls of water, so as to secure more food.