124 THEORY OF THE EARTH. 



of the bones are very little changed ; their con* 

 nexions and articulations, and the form and struc- 

 ture of the large grinding teeth, are invariably the 

 same. The small size of the tusks in the domes- 

 ticated hog, compared with the wild boar of which 

 it is only a cultivated variety, and the junction of 

 its cloven hoofs into one solid hoof, observable in 

 some races, form the extreme point of the dif- 

 ferences which man has been able to produce 

 among herbivorous domesticated quadrupeds. 



The most remarkable effects of the influence of 

 man are produced upon that animal which he has 

 reduced most completely under subjection. Dogs 

 have been transported by mankind into every 

 part of the world, and have submitted their ac- 

 tions to his entire direction. Regulated in their 

 sexual unions by the pleasure or caprice of their 

 masters, the almost endless varieties of dogs differ 

 from each other in colour ; in length and abun^ 

 dance of hair, which is sometimes entirely want- 

 ing ; in their natural instincts ; in size, which va- 

 ries in measure as one to five, amounting, in some 

 instances, to more than an hundred fold in bulk ; 

 in the forms of their ears, noses, and tails ; in the 

 relative length of their legs ; in the progressive de- 

 velopement of the brain in several of the domes- 

 ticated varieties, occasioning alterations, even in 

 the form of the head ; some of them having long 

 slender muzzles with a flat forehead ; others having 

 short muzzles, with the forehead convex, &c. inso- 

 much that the apparent differences between a mas- 



