Class 6. Mammalia. Order 7. Sirenia. 



513 



the females they are never outj but a horny plate covers the jaw 

 above and below; canines are absent; the molars are small with 

 transverse ridges ; the Manatee has about ten in each half of the jaw, 

 the Dugong fewer : the stomach is complicated in structure* 



The Sirenia are herbivorous and feed upon alg^; they are of 

 considerable size (existing forms 3 m. to 5 m.), and are found on sea 

 coasts and in rivers. The only representatives now living are the 

 Manatee {Manatus), on the Atlantic coasts of Africa and America 

 (and the adjacent rivers) ; and the Dugong {Malicore dugong), in 

 the Indian Ocean. The gigantic, edentulous Rhytina, Steller's 

 Cow [Rhytina stelleri), is now exterminated. Until the last century 

 it was found in the North Pacific. 



Order 8. Carnivora. 



The Carnivora constitute a large group, including numerous genera 

 and species, which exhibit great diversity both in structure and also 

 in habits ; certain characteristic features run through the whole 

 group, and all the members are reducible to a common type. 



This is particularly evident with regard to the dentition, 

 which is most easily comprehended if that of the D o g is considered 

 first ; for that of other members of the group may be regarded as 



Fig. 411. 



Fig. 412. 



Fig. 411. The teeth of the permanent dentition of the left half of the skull of a Dog, 

 and the milk dentition of the same, the latter shaded. — Orig. 



Fig. 412. The same of a C at .—Orig. 



variously modified from it. There are, then, on each side of the 

 upper jaw of the Dog, three incisors (of which the third and outer- 

 most is larger than the others), one conical curved canine and six 

 molars (four premolars and two molars) . The three anterior upper 



* "With regard to the skeleton it may be noticed that the lower jaw is very large 

 and heavy, very unlike that of the Whale's, and this is true also for the rest of the 

 skuU, 



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