exists, as there is only one vertebra in front of the shoulders (Fig. 252), although most vertebrates have seven neck (cervical) vertebræ. There are no tail (caudal) vertebræ, even in the tadpole state of frogs and toads.
The head appears triangular in shape when viewed from what direction? The head of a frog is more pointed than the head of a toad. Is the skull a closed case of broad bones or an open structure of narrow bones? (Fig. 252.)
Describe the mouth. Observe the extent of the mouth opening (Fig. 251). Are teeth present in the upper jaw? The lower jaw? Are the teeth sharp, or dull? Does the frog chew its food? Is the tongue slender or thick? (Fig. 251.) Is it attached to the front or the back of the mouth? In what direction does the free end extend when the tongue lies flat? Is the end pointed or lobed? How far out will the tongue stretch? For what is it used? Why is it better for the teeth to be in the upper jaw rather than in the lower jaw? That the teeth are of little service is shown by the fact that the toad with similar habits of eating has no teeth. Will a toad catch and swallow a bullet or pebble rolled before it? The toad is accustomed to living food, hence prefers a moving insect to a still one.
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Fig. 251.—Head of Frog.
The Senses.—Compare the eyes with the eyes of a fish in respect to position and parts. Are the eyes protruding or deep-set? Touch the eye of a live frog. Can it be retracted? What is the shape of the pupil? The color of the iris? Is the eye bright or dull? What probably gave rise to the superstition that a toad had a jewel in its head? Is there a third eyelid? Are the
