440 MAMMALIA. 



Mammalia. Ungulates have all four limbs touching the ground 

 by the last toe-joint only, and that joint is enshrouded in a case 

 or hoof of horn (except Hyracoidea). The hoof is an expanded 

 nail. In no ungulate do we find more than four toes to each 

 limb. Clavicles absent. There are always two sets of teeth, 

 milk-teeth and permanent teeth ; the molars have always hroad 

 crowns (fig. 211), adapted for chewing and grinding vegetation, 

 upon which all the Ungulata live. The Ungulata are divided 

 into two sections : — 



1. Perissodadyla. — Toes always odd in number on hind feet, 



either one or three (fig. 208, B). Stomach simple. 

 Fibula articulates with astragalus. 



2. Artiodactyla. — Toes always even in number, being two or 



four to each foot {A). Stomach complex. Fibula 

 articulates with astragalus and calcaneum. 



Section 1. Perissodactyla. 



This section includes the horses, tapirs, and rhinoceros, in 

 which the stomach is simple, and a large caecum present as seen 

 in the horse. The hind-feet are odd-toed in all perissodactyla, 

 and the fore- feet in many. The third toe always forms the 

 functional axis. The dorso - lumbar vertebras are never less 

 than twenty-two in number, and the femur has always a third 

 trochanter. If horns are present, they never have bony cores 

 as in cattle. 



We need refer to one family only, the Equid^, Solid- 

 UNGULA, or SoLiPEDS. The Equidas are the horses, asses, and 

 zebras. The features of these can be taken from the descrip- 

 tion of the horse already given. All our domestic varieties are 

 considered one species, Equus caballus. At Solutre are immense 

 bone-beds with horse remains : the descendants of these are 

 probably the Ardennes horses, one of the long-headed races 

 which seem very similar to the fossil ones of Solutre. From 

 these also are descended the semi- wild horses in the delta of 



