520 LAND MAMMALS IN THE WESTERN HEMISPHERE 



1. Canidce. Dogs, Wolves, Foxes, etc. 



This family, which may with convenience be called simply 

 dogs, is at present the most widely distributed of the families of 

 Fissipedia, occurring in every continent, even Australia, 

 and ranging through all climates almost from pole to pole. 

 They are a singularly homogeneous family and show few 

 differences of structure ; such differences as there are affect 

 chiefly the number and size of the teeth and external char- 

 acters, such as the size of the ears, length and colouring of the 

 hair, etc. The many domestic breeds are not here considered. 

 Almost alone among the Fissipedia the dogs capture their 

 prey by running it down, and they are endowed with remark- 

 able speed and endurance. The entire organism, especially 

 the limbs and feet, are adapted to cursorial habits. 



For the purpose of comparison with the extinct genera of 

 the family, some account of a wolf will suffice. The wolves, 

 like most other members of the family, have a larger number 

 of teeth than is usual in the suborder, as appears from the 

 formula : if, c\, pi, m|,x2 = 42, that is to say, only the third 

 upper molar has been lost from the typical number, though the 

 third lower is very small and seemingly on the point of dis- 

 appearance (Fig. 44, p. 93). The upper sectorial tooth, 

 the fourth premolar, has its shearing blade made up of two 

 sharp-edged cusps, one behind the other, and there is a small 

 internal cusp carried on a separate root ; the upper molars 

 are triangular and tritubercular and are used for crushing. 

 The lower sectorial, the first molar, has an anterior blade of 

 two shearing cusps, with the remnant of a third, and a low, 

 basin-like posterior "heel." 



The skull is characterized by the long face and jaws and 

 by the structure of the auditory region ; the tympanic bones 

 are inflated into large oval bullae, which are hollow and un- 

 divided, and the external opening of each is an irregular hole, 

 without tubular prolongation. There is an alisphenoid canal 



