VERTEBRATA: MAMMALIA. 743 



be drawn between the Plantigrade and Digitigrade sections of 

 the Carnivora, since many forms (e.g., Mustelida and Viver- 

 ridce) exhibit transitional characters, and it has even been pro- 

 posed to place these in a separate section, under the name of 

 Semi-plantigrada. Moreover, the Mtislelidce and Melidcz are 

 so nearly allied that they can with difficulty be kept apart. 



The first family of the Digitigrada is that of the Mustelida 

 or Weasels, including a number of small Carnivores, with short 

 legs, elongated worm-like bodies, and a peculiar gliding mode 

 of progression (hence the name of Vermiformes, sometimes 

 applied to the group). The dental formula of Mustela proper 

 is 



33 i i 44 22 



In the nearly-allied genus Putorius (fig. 430) there is a prae- 

 molar less above and below. 



Among the best known of the Mustelidcz are the common 

 Weasel (Putorius vulgaris], the Polecat (Putorius fatidus\ and 



Fig. 430. Skull of the Polecat (Putorius fcetidus). 



the Ferret (Putorius furo), the last being usually regarded as 

 an albino variety (now permanent) of one of the Polecats. 

 It is really an African form, but it has been long domesticated 

 in Europe. Nearly-allied types are the Ermine or Stoat (Pu- 

 torius erminea), and the Minks (P. vison and P. lutreold] of 

 North America and Europe. Among the species of Mustela 

 proper may be mentioned the Pine-marten (M. martes) and 

 Stone-marten (M. foind] of Europe and Asia, the Pekan or 

 "Fisher" (M. Pennantii) of North America, the true Sable 

 (M. zibellina) of northern Asia, and the American Sable (M. 

 Americana). The Mustelida are of commercial importance 

 as yielding beautiful and highly- valued furs, the skins of the 



