MAMMALIA. 443 



Nothing is more striking than the characters by which it is distinguished 

 from all others, namely, a single hoot' with an apparently single toe to each 

 foot ; but on the skeleton, on each side of the metatarsus and metacarpus, 

 there are spurs representing two lateral toes. Only one genus of the pre- 

 sent family is found in the actual fauna and with but comparatively few 

 species, whilst in the tertiary de])Osits we find at least as many extinct 

 species together with extinct genera. 



The genus Mjuus is characterized by six incisors in each jaw, the crowns 

 of which, at an early age, are marked with a fossula, and six molars through- 

 out, with a square crown, marked by lamina of enamel which dip into 

 them, with four crescents, and in the upper ones, with a small disk on the 

 inner edge. The male has also two small additional canines in the upper 

 jaw, sometimes in both, which arc almost always wanting in the female. 

 Between these canines and the first molar is a free space corresponding to 

 the angle of the lips where the bit is placed, and by which, as Cuvier 

 remarks, man alone has been enabled to subdue and tame this powerful 

 animal. 



The common horse, Equus caballus (pi. 110, ßg. 4), is the n"kost import- 

 ant of all the animals that man has subdued. His associate in the chase, 

 in war, and in ihe operations of agriculture, of arts and commerce, or raised 

 for luxury, the horse has received by that perpetual contact a noble port 

 and proud carriage. The horse, however, does not exist in a wild state at 

 the present time, except in those places where horses were formerly domes- 

 ticated and set at liberty, as in Tartary and America. They live in troops, 

 each of which is conducted and defended by an old male. The young- 

 males are forcibly expelled as soon as they have reached the age of puberty, 

 and follow the troop at a distance until they are joined by some of the 

 younger mares. They propagate at four years ; the pei'iod of gestation is 

 eleven months. The age of horses is known by the incisors. The milk teeth 

 begin to grow about fifteen days after the colt is foaled ; at two years and 

 a half the middle ones are replaced ; at three and a half the two succeeding 

 ones ; at four and a half the outermost, or the corners. All these teeth, 

 with an originally indented crown, gradually lose that mark by detrition. 

 When seven or eight years old they are entirely effaced, and the horse is 

 no longer marked. The life of the horse seldom extends beyond thirty 

 years. This animal varies very much in size and color. The principal 

 races exhibit sensible differences in the form of the head, in their propor- 

 tions, and in their fitness for the various uses to which they are applied. 



1. Thfe most beautiful and swift is the Arab (of which 2Ü. 110, ßg. 6, 

 represents the mare with her colt, and ßg. 7 the stallion), which has been 

 instrumental in mproving the Spanish race., and in connexion with the; 

 latter has contributed to form the English race; the Barbary, Persian, 

 Circassian, and Turkish horses descend from the Arab. The Arab horse 

 inhaVjits western Asia and northern Africa, where it is found of medium 

 size. 



2. The northern horse^ rather small than large, light, docile, swift, hard- 

 working, enduring, and satisfied with little and common food. The Tartar, 



64Y 



