We must not, however, imagine that the snake is at a disadvantage because he has lost so many parts which other reptiles possess. On the contrary, he has most probably lost them because he can do better without them. The transparent tough skin over his eye is a far better protection in narrow rugged places, and among brakes and brambles, than a soft movable eyelid; and if he does not see as well as the crocodile, he has a most delicate organ of touch in his long, narrow, forked tongue, with which he is constantly feeling as he goes, touching now on one side, now on the other, each object he comes near, and drawing the tongue in at every moment to moisten it in a sheath at the back of his throat. A breast bone, moreover, would have been a decided hindrance to him, for he wants the free use of all his ribs; and as to the loss of his legs--in the place of four he has often more than two hundred. For all along his backbone, except just at the head and tail, a pair of ribs grow from each vertebra, being joined to it by a cup-and-ball joint (_c_ and _b_, Fig. 26), and the muscles between them are so elastic that the ribs can be drawn out so that the body seems to swell, and then drawn back towards the tail. In doing this they strike the ground and the snake moves forwards, just as a centipede does on its hundred legs. It is worth while to take our harmless Ringed Snake in your hand to feel this curious movement to and fro of the ribs, and to notice how the creature forces itself through your grasp. Moreover, you will learn at the same time one use of the broad single plates under the snake’s body (see Fig. 27), for they, like all the scales, are loose from the skin on the side towards the tail; and as they are fastened by muscles to the ends of the ribs, you will find that at each movement they stand up a little like tiles on a roof, and their edges coming against your hand help to drive the snake forward. Another thing you will learn if the snake does not know you, and that is how strangely they hiss, often with their mouth closed, while their whole body seems to quiver. This is very puzzling at first, till you learn that one of their lungs has shrunk up, and the other is a very long and narrow bag stretching nearly the whole length of the snake’s stomach, and the hissing sound is made by drawing in and forcing out the air from this long bag. [Illustration: Fig. 27. Common Ringed Snake.[84] Where the body is coiled the single under plates are seen.]