MAMMALS 



309 



Skull of a porcupine, a rodent. Notice the large overlap- 

 ping incisor teeth. Compare with teeth of dog (see 

 page 313). 



molars in your own 

 mouth. Do you find teeth 

 of any other shape than 

 those just described? 



Compare the position 

 and shape of the eye with 

 that of your own. Is the 

 eye protected in any 

 other way than by posi- 

 tion ? Note the bony eye 

 socket in the skull, the 

 lids (number), and any 

 other adaptations. Touch 

 the eye very lightly and 

 see the third or "wink- 

 ing" eyelid (the nictitat- 

 ing membrane). 



Notice the shape and position of the external ear. Compare with the 

 head in length. The external ear collects the sound waves and sends 

 them into the internal ear, the true organ of hearing (see page 421). 

 Test the animal's response to sounds, especially when the maker of the 

 sound is hidden. Is the hearing of the rabbit acute? (The above 

 problem makes a good series of home experiments.) 



Notice the mobility of the nose, especially when the animal is sniffing. 

 By means of some strongly smelling substances, determine whether the 

 rabbit easily perceives odors. Try to determine whether the saying that 

 the whiskers of a cat or rabbit are used to smell with has any foundation 

 in fact. Notice whether the hairs move at the same time the odor is 

 presented. 



Skeleton. — The rabbit is provided with a bony skeleton which gives 

 support to the muscles and also protects the delicate organs of digestion, res- 

 piration, etc., under the 

 ribs. Compare with the 

 skeleton of man in this 

 respect (see page 372), 

 The bones of the skele- 

 ton may be divided into 

 two groups as in man, 

 — those of the axial 

 skeleton, the vertebrae, 

 and bones of the head; 

 and those of the append- 

 ages, including the pec- 

 toral and pelvic arches, 

 where the appendages 

 are attached to the axial 



The skeleton of a monkey, a typical mammal. 



skeleton. Part for part and almost bone for bone the skeleton of the rabbit 

 may be compared with that of man (see page 372) . The chief differences 

 exist in the appendages, where the erect animal, man, has the bones of the 



