THE SKELETON IN MAMMALIA. THE TEETH. 437 



only rodents which have Avell developed deciduous incisors, 

 though a vestigial milk incisor has been described in the 

 Mouse (Mus musculus). The last upper molar of Hydrochaerus 

 is very complicated, its structure approaching that of the teeth 

 of Elephants. 



CARNIVORA have the teeth rooted and markedly diphyodont 

 and heterodont. The canines are greatly developed, and the 

 incisors are small. 



In CARNIVORA VERA the incisors are almost always . The 

 fourth upper premolar and first lower molar are differentiated 

 as carnassial teeth (see p. 436), and retain fundamentally the 

 same characters throughout the suborder. The upper car- 

 nassial (fig. 84, I. II. III.) consists of a more or less compressed, 

 commonly trilobed blade borne on two roots, with an inner 

 tubercle borne on a third root. The lower carnassial has only 

 two roots ; its crown consists of a bilobed blade with generally 

 an inner cusp, and a heel or talon (fig. 84, 4) behind the blade. 



The most thoroughly carnivorous type of dentition is seen 

 in the ^luroidea, and especially in the cat tribe (Felidae). In 



31 31 

 the genus Felis the dental formula is i = c = pm - m - , total 30. 



The incisors are very small, so as not to interfere with the 

 action of the large canines, the lower carnassial is reduced to 

 simply the bilobed blade (fig. 84, IV), and the cheek teeth are 

 greatly subordinated to the carnassial. The extinct Machae- 

 rodus has the upper canines comparable in size to those of the 

 Walrus. 



The Civets and Hyaenas have a dentition allying them 

 closely to the cats. The hyaena-like Proteles has, however, 

 the grinding teeth greatly reduced. 



.31 4 2 



In the Cynoidea 1 the general dentition is i = c = pm - m -= , 



o 1 4 o 



total 42. This differs from the regular mammalian dentition 



1 See T. H. Huxley, "The dental and cranial characters of the 

 Cauidae," P. Z. S., 1880, p. 238. 



