I shall spend some little time in explaining to you each of these particulars, that you may see how wisely all the parts of living things are framed to supply their wants, and adapt them to the circumstances in which they are placed. The head was not very different from that of a crocodile, or lizard, in its general shape. The teeth were precisely like those of a crocodile, and grew up in the same manner. Creatures of this sort lead a ruffian sort of life, always biting something or other, and as they live very much in the dark at the bottom of the water, perhaps now and then snap at a stone or a piece of hard wood by mistake, and often break their teeth; and in order therefore to keep them in constant repair, they have a fresh set once a year, or at very short intervals, so that they are always growing. The young tooth _a_, springs up inside the old one _b_, till it becomes so large that it splits its predecessor, and the pieces fall off, just as the covering of some sorts of buds falls off as the flower expands, as you will see in this cut, representing one of the fossil teeth. [Illustration] You must have noticed in the picture the great length of his snout. In a jaw-bone of such amazing length which was to be applied to such violent purposes, it was necessary there should be great strength. There were two ways of obtaining this: one would have been by having the bones very hard and stout; but this would not do, because they would then have been so heavy that the animal would have found difficulty in raising his head to the surface of the water for the purpose of breathing, since it would have overbalanced the other part of his body. The other contrivance, which was the one adopted by the wisdom of the Creator, was to make the jaws consist of several thin bones, _a_, _b_, _c_, _d_, strongly bound together, and terminating in succession like the plates of steel of which a carriage spring is made. There are accordingly six of these bones thus disposed. [Illustration] But this was not all, the principal middle bone marked _b_, instead of having its fibres run straight, parallel with the others, had them placed in a slanting position, and thus there was additional firmness given to the jaw by what ship-builders would call _diagonal bracing_, a contrivance that you may often see used in the construction of houses and ships. If you have ever seen a crocodile open its mouth, and then snap together its long thin jaws, so as to make you start with the noise, you will see how necessary all these contrivances must be for him and the Icthyosaurus, whose jaws were still thinner, to prevent them from breaking their bones.