I3O ANIMAL BIOLOGY 



exists, as there is only one vertebra in front of the shoul- 

 ders (Fig. 252), although most vertebrates have seven neck 

 (cervical) vertebrae. There are no tail (caudal) vertebrae, 

 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 month. 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 

 FIG. 251. HEAD OF FROG. 



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 simi- 

 lar 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. 



The Senses. Compare the eyes with the eyes of a 

 fish in respect to position and parts. Are the eyes pro- 

 truding 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 



