114 



VERTEBRATA: MAMMALIA, 



lience the Sirenia and Cetacea are sometimes grouped to- 

 gether, and the group thus formed is called the Mutilata. 



The Sirenia, however, differ from the Whales in many 

 respects, both in structure and in habits. The brain 

 of the Sireuians is narrow ; their neck is of moderate 

 length, and its second vertebra has a tooth-like process ; 

 their only limbs, the forward ones, are moderately long, 

 and flexed at the elbow ; the mammae are upon the breast ; 

 they have molar teeth with flat crowns adapted for grind- 

 ing vegetation, and have corresponding herbivorous 

 habits. They inhabit the warmer parts of the ocean, 

 near the shores, and often ascend large rivers. They even 

 leave the water and crawl upon the shore to feed upon the 



f IG. 122. 



Sea-Cow, Momatus. 



land vegetation ; and this fact caused them to be called 

 u Herbivorous Whales." They attain the length of ten to 

 twenty feet. 



Some kinds of the Sirenians, as the Sea-Cows (Manatus), 



