(a).—Open the jaws widely, and examine the inside of the mouth. Notice how the rounded eyeballs project into the mouth-cavity when they are pressed from the outside. Pass your finger-end round the margins of the jaws, and feel the row of fine teeth borne by the upper jaw; the lower jaw is destitute of teeth. Feel also, in the roof of the mouth, two small patches of teeth (Vo., Fig. 216); these are carried by small bones called the vomers, and are therefore called the vomerine teeth. Just to the outside of the vomerine teeth and in front of the eyeball, notice on each side the internal opening of the nostril (Ch., Fig. 216); pass into one nostril a stiff bristle, and observe that it emerges at the external nostril. Pull forward the tongue (T, Fig. 216) and observe that it is attached at its front end; feel how sticky the tongue is. Behind the eyes, and at the angles of the jaws, notice the openings of the Eustachian tubes (E, Fig. 216); push a stiff bristle into one and observe, from the outside, that the end of the bristle presses the inner surface of the ear-drum. [Pg 334] (b).—If the roof of the mouth has dried, moisten it with water, and place a very small cork-shaving or a tiny snip of paper on it, far back between the eyeballs. Notice that the shaving travels slowly down the throat. This experiment ought to be made soon after the frog has been killed. 6. The bones.—Feel, through the body-wall, the various parts of the skeleton, making out the skull, backbone, limb-bones and their manner of attachment, and breast-bone (protecting the heart). Observe the absence of ribs. 7. The skin.—Examine the skin of the dead frog, and notice that it is damp or even somewhat slimy, and that it differs from the skin of a mammal or bird in being naked, bearing neither hairs, feathers, nor scales. Pinch up the skin, and notice how very loosely it is attached to the underlying body-wall. Snip through the thin skin, turn it back from the body-wall, and see the network of blood-vessels upon its inner surface.