444 ZOOLOGY. 
Russian, Polish, Lithuanian, and Swedish horses descend from the same 
stock, to which also belongs the Siberian horse (pl. 109, fig. 11), which 
during winter is covered with very thick and long hair. 
3. The West European horse is large, less enduring, however, than eithase 
of the preceding ones: here belong also the Spanish horse, the Sicilian, 
the French, English, Hungarian, Transylvanian, German, and _ Italian. 
Pi. 110, fig. 5, represents the Norman team horse, supposed to be of Danish 
breed. It is raised in lower Normandy. 
The ass, Equus asinus (pl. 110, fig. 2), is another species of the same 
genus, originally from the great desert of central Asia, and still to be found 
there in a wild state, in innumerable troops, ranging from north to south, 
according to the season. The ass has been domesticated like the horse, 
and renders very great service to man, whom it has followed through 
almost all his migrations. A cross breed between the ass and the mare is 
called a mule, well known to the ancients, who called it Mulus, or the 
mule proper (p/. 110, fig. 3), produced by the male ass and female horse ; 
whilst they termed Hinnus the mule arising from the union of the male 
horse with the female ass. Mules are very valuable animals, and capable 
of being employed where the horse and ass would be useless. The mule 
stock cannot perpetuate itself, for it soon degenerates when it is not sterile. 
At any rate, sterility declares itself after the second or third generation, 
To keep the stock perfect. the parent of both species, the horse and the ass, 
must always breed together. 
The zebra, Equus zebra (pl. 110, fig. 1), originally from the south of 
Africa, has never been domesticated, and seldom tamed by man. It is 
nearly of the same form as the ass, but regularly marked with black and 
white transverse stripes. A female zebra has successively produced an 
offspring with the horse and the ass. 
The dzigguetai (Hquus hemionus), intermediate by its proportions between 
the horse and the ass, lives in troops in the sandy deserts of central Asia. 
It is of an isabella or light bay color, with a black mane and a dorsal line of 
the same color. Supposed to be the wild mule of the ancients. 
The couagga and the onagga or dawn are two other wild species of 
horses. 
If the American continent has no indigenous horse in the present fauna, 
the remains of several species are found in the tertiary deposits of North 
and another in South America. A few fossil species have been discovered 
in Europe and in the Sivalic Mountains in Asia. Two extinct genera of 
this family are already known. 
The genus Hippotherium differs from equus by the structure of the 
molars, the laminee of which are much more complicated, forming nume- 
rous zigzag folds. It forms also a transition towards the pachyderms 
proper, inasmuch as the anterior feet possess the rudiments of a fourth 
finger or toe. Several species have been described as belonging to Europe, 
but more recent observations seem to reduce their number to one, which 
lived in numerous individuals in the centre and south of Europe during the 
meiocene period up to the diluvium. 
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