130 MAMMALIA ORDER VI.UNGULATA. 



has a high-bred tone in his deportment, a high-actioned step when it trots 

 freely over the rocks and sand, with the speed of a horse when it gallops over 

 the boundless desert. The specimens now in the Zoological Gardens will 

 enable any one to perceive the character of the animal as it was before being 

 altered by generations of captivity." The bray of the Abyssinian is identical 

 with that of our common ass, and Darwin notes the marked aversion to walking 

 across a brook, which characterises the domestic donkey, as indicating its 

 derivation from a desert-haunting animal ; as also does its pleasure in 

 rolling in the dust. The Somali ass differs from the ordinary African 

 form in its more greyish colour, the absence of the cross-stripe over the 

 shoulders, the very slight indication of the spinal stripe, and more especially 

 in the numerous black markings on both front and hind-legs. Jt has, like- 

 wise, smaller ears and a longer mane. It may be a matter of doubt whether 

 these differences are of specific value, but they probably only indicate a 

 variety. Of this form Mr. Lort Phillips writes that "on March 22, 1884, 

 when about 20 miles to the west of Berbera, we fell in with a small herd of 

 wild asses. After a long and tedious stalk I succeeded in bagging one, which 

 turned out to be of quite a new species to me, having no mark whatever on 

 the body, which was of a beautiful French grey colour. On its legs, however, 

 it had black stripes running diagonally. I have, unfortunately, lost the book 

 in which I put its measurements, but it was a superb creature, and stood 

 quite 14 hands at the shoulder j our Berbera horses looked quite small in 

 comparison." 



The two species of hippopotamus, both of which are now confined to Africa, 

 and may be referred to the genus Hippopotamus, bring us to the fourth and 

 last sub-ordinal division of the Hoofed Mammals, which far 

 The Hippopot- outnumbers the whole of the other three put together, both 

 ami. Family as regards families, genera, and species. From the fact that 

 Hippopotamidte the two toes corresponding to the third and fourth digits of 

 the human hand and foot are of equal size, and symmetrical 

 to a vertical line drawn between them, this group has been appropriately 

 named the Artiodactyla, or Even-toed Ungulates. Whereas, however, in 

 some species, such as the giraffe, only these two digits are present ; in others, 

 like the hippopotami, there are four functional digits ; while in yet others, as 

 the oxen, the middle *pair alone are functional, and the lateral ones much 

 reduced in size, and of no functional importance. In the peccaries the hind- 

 foot is unique among the sub-order in having only three toes. Although the 

 structure of the feet forms the prime distinction between the Artiodactyla 

 and Perissodactyla; there are many other points of difference between the 

 two groups, a few of which may be mentioned. As regards the teeth, 

 the premolars of the Artiodactyla are almost invariably of simpler structure 

 than the molars ; while the last lower molar is nearly always composed 

 of three transverse lobes, whereas in all the living representatives of the 

 Perissodactyla it is two-lobed. The femur or thigh-bone of the latter 

 group is always provided with a large projecting process in the upper 

 half of the shaft known as the third troehanter, which is invariably absent 

 in the one under consideration. Again, in the ankle-joint the huckle-bone, 

 or astralagus, of the Artiodactyla has its lower articular surface divided 

 into two nearly equal facets, whereas in the Perissodactyla such surface is 

 single. There are many other minor points of difference, but those given 

 are amply sufficient to distinguish between the two sub-orders. 



The hippopotami are the most primitive and least specialised of the existing 



