1426 CLASS MAMMALIA. 



mention must be made of the alisphenoid canal, which is a short 

 bony channel situated in the alisphenoid bone immediately on the 

 outer side of the pterygoid. The existing representatives of this 

 suborder have been divided into three sections — the Arctoidea, 

 Cynoidea, and ^Eluroidea ; but extinct forms show such a complete 

 transition between the three that it is impossible to adopt any divi- 

 sions of higher rank than families, and scarcely any two writers agree 

 as to the limits of the latter. It is, moreover, very doubtful whether 

 the Arctoidea is really a natural group. When, indeed, we go back 

 to the Upper Eocene or Lower Oligocene, where this suborder is 

 first definitely known, we find that Bears pass imperceptibly into 

 Dogs, Dogs into Civets, Civets into Hysenas and Cats, while Weasels 

 appear to be related to the Civets ; and the principles adopted in the 

 classification of recent forms consequently fail to enable us to make 

 any really satisfactory arrangement. 



Family Mustelid^e. — This family comprises the Sea-Otters, 

 Otters, Badgers, and Weasels. In all existing forms the skull has 

 no alisphenoid canal ; there is never more than one upper true 

 molar, and the lower true molars are nearly always two, although 

 reduced to one in Mellivora. The upper true molar has its inner 

 tubercular portion wider than the outer or cutting moiety (fig. 1306), 

 this feature being most developed in the Otters (fig. 1303); and the 



Palate of Lutra cinerea ; India. 



cusps of the blade of the lower carnassial are comparatively low (fig. 

 1308). The palate is comparatively wide, and the premolars are 

 somewhat crowded together; while the auditory bulla has no 

 septum, and is usually, but slightly, inflated. It is suggested by 

 Dr Scott that the Mustelidce are a branch from the primitive Viver- 

 ridce, and there is considerable evidence in favour of this view, 

 which, if true, at once breaks up the Arctoidea. 



The existing Lutrine section may be palaeontologically divided 

 into Lutra and Enhydra ; the latter being a marine form unknown 



