226 VERTEBRATA. MAMMALIA. 



the strict geographical limits which confine the ter- 

 restrial Mammalia. It appears, however, that the 

 species which frequent the Northern and Southern 

 seas are distinct, and some, especially of the smaller 

 kinds, seem very limited in their locality. 



Before we come to the Marine Cetacea, we meet 

 with a few species which are evidently intermediate 

 between animals so different as these and the Quad- 

 ruped Mammalia. They are usually known as the 

 Herbivorous Cetacea. The order to which they bear 

 the closest affinity is the Pachydermata. The great 

 size of many species of that order, the naked skin, the 

 small eye, the wide mouth, the short flattened tail, 

 and even the tendency, as in the Hog, to form fat 

 on the surface of the body, all mark the transition. 

 But there is a fossil animal among the Pachyderms, 

 named the Deinotherium,* from whose lower jaw two 

 tusks arose as in the Hippopotamus, but then curved 

 downward to an enormous size. It is supposed to 

 have been even still more aquatic than the last-named 

 animal, and is considered the uniting link between 

 it, and those of which we are about to speak. 



Manatusfi the Cow-whale. 



Having flat grinders, these animals feed on the 

 aquatic plants that grow in abundance at the mouths 

 of tropical rivers, and even, sometimes, crawl on 

 shore to feed. J When seen in this situation, the broad 



* Ativof, deinos, terrible, and ^/v, tJierion, a wild beast, 

 t Manus, a hand. + Cuvier. 



