12 



THE HORSE 



ridged grinding surfaces, and they have a very com- 

 pletely developed set of milk-teeth, which are not changed 

 until the animals have nearly attained maturity. Their 

 limbs are adapted for carrying the body in ordinary terres- 

 trial progression, and are of very little use for any other 

 purpose, such as flying, climbing, seizing prey, or carry- 

 ing food to the mouth. They have no clavicles or collar- 

 bones. Their toes are provided with blunt, broad nails, 

 which in the majority of cases more or less surround 

 and enclose their ends, and are called hoofs. Leaving 

 aside certain forms which are not so nearly related to 

 the subject of this memoir as to concern us further and 

 which are nearly all extinct, the majority of the ungu- 

 lated animals have been throughout the whole of the 

 Tertiary period separated into two perfectly distinct sec- 

 tions, differing from each other not only in the obvious 

 characters of the structure of their limbs, but in nume- 

 rous important points in other portions of their organisa- 

 tion, such as their skull, vertebral column, teeth, diges- 

 tive organs, &c. The characters of these' two groups, 

 first indicated by Cuvier, were thoroughly established by 

 Owen, by whom the names by which they are now gene- 

 rally known were proposed. These are Artiodactyla, or 

 even-toed, and Perissodactyla^ or odd-toed. 1 



It is only by studying the fundamental type of 



1 From the Greek artios, even in number, and j^^sos, uneven ; 

 combined with daktylos, finger or toe. 



