680 Comparative Morphology of Chordates 



Fig. 508. Elephant-shrew, an insect i\ ore. (Courtesy, American Museum of 

 Natural History, New York.) 



In many ungulates and carnivores the external surface of the snout 

 plays an important sensory role in conjunction with the internal organs 

 of smell. The skin of the anterior region of the snout is scantily covered 

 by hair and richly supplied with glands which keep its surface moist, 

 thus making it highly sensitive to currents of air. By this means the 

 animal is able to sense the direction of the wind and is thereby made 

 aware of the location of the object which is being smelled. A deer 

 hunter knows that he must not let the animal "get wind" of him. 



The eye is one of the least changeable of vertebrate organs. In 

 fishes it reaches so high a degree of efficiency that it is not susceptible 

 of great changes of structure, except degenerative, in other vertebrates. 



The mammalian eyeball and its associated structures are lodged 

 in an orbit whose closely fitting bony wall nearly or quite surrounds 

 the eye, giving it a degree of external protection which obviates the 

 necessity of developing skeletal structures in its sclerotic layer. 



The size of the eyeball necessarily varies with that of the animal, 

 but not proportionately. Relative to size of body, eyes of large mam- 

 mals are smaller than those of small mammals. In general, larger eyes 

 give keener vision, but size is not the only factor involved and the 

 smaller eyes of small animals are not necessarily of low efficiency. 

 Animals of nocturnal habits generally have especially large eyes with 

 disproportionately large pupils. 



In fishes the external face of the eyeball is usually nearly flat and 



