ii6 BRITISH MAMMALS 



walruses, seals). Besides the special adaptation to a life in the 

 water which affects the Pinnipedia, there is a further marked 

 difference between them and the terrestrial Carnivores at the 

 present day. The Fissipedia have developed a pair of carnassial 

 or powerful cutting teeth from out of the grinders in both jaws. 

 In the upper jaw this carnassial tooth is the fourth premolar. In 

 the lower jaw it is the first true molar. Now in the seals there 

 is no special differentiation, for crushing or tearing purposes, of 

 either the premolars or molars. This feature of the carnassial 

 teeth, however, is scarcely developed at all in Otocyon, and but 

 little developed in aberrant forms of the Raccoon family and in 

 the Bears. 



The Carnivora are for the most part five-toed, and never 

 have less than four toes on each foot. Their teeth are always 

 rooted. The incisors are almost invariably three pairs in each 

 jaw, except in the case of the seals. The molar and premolar 

 teeth are generally narrow, and divided longitudinally into sharp 

 cusps ; but if broad, flat, and set with tubercles, they are never 



seem, therefore, as though, to account for the four molars of certain 

 dogs co-existing with four premolars, we must go back for the origin of 

 the modern Carnivora to a proto-mammalian type ancestral to Marsupials, 

 Creodonts, and other mammalia. Until some Creodont is discovered with 

 four molars, it will be difficult to believe that the existing Carnivora have 

 descended from that group. The Creodonts, like the carnivorous Marsupials, 

 probably pursued a parallel line of development as predatory flesh-eating 

 mammals. It might, perhaps, assist the reader of these pages who is not 

 well acquainted with the nature of teeth, to be told that the distinction 

 between molars and premolars is this. Premolars have at any rate for the 

 last three of the series "milk" predecessors in most mammals, whereas true 

 molar teeth have no predecessors. This distinction scarcely applies to some 

 teeth in Marsupials, whose " milk " dentition has been almost suppressed. 

 Molars and premolars, therefore, in those creatures are generally distinguished 

 by shape ; but, even in this case, what is equivalent to the fourth premolar in 

 a Marsupial has a "milk" predecessor. As regards the fourth true molar 

 tooth, it is found in some Edentates, living and extinct ; in extinct Sirenians 

 (ancestors of the dugong and manati) ; and perhaps occurred in the earliest 

 Primates. It makes its appearance even in the human species occasionally, 

 and as a sport this happens much more frequently in the black Australian 

 and the Negro races than with Europeans. 



