40 



THE ODD-TOED UNGULATES. 



inhabitants of the stony deserts of Africa and 

 Syria were regarded as rodents, and the older 

 zoologists were not a little astonished when 

 Cuvier declared that they had a great resem- 

 blance to the rhinoceroses. Their possession 

 of a zonary placenta induced many more 

 recent naturalists to rank them with the ele- 

 phants. Now that we are acquainted with a 

 considerable number of fossil ungulates of 

 small size, both odd-toed and even-toed, the 

 persistence of a genus, which is about equal 

 in size to such old genera as Tapirulus, has 

 nothing so very remarkable about it as ap- 

 peared to be the case when only the large Per- 

 issodactyla of the present day were known. 



In their external appearance the Hyracida 

 resemble small marmots, the bobaks of the 

 Russian steppes, and the prairie dogs of North 

 America (Cynomys). The short fat body 

 ending with a thick head, pointed in front 

 and 'supported by two pairs of short slender 

 limbs, while at the other end there is only 

 a short stump representing a tail, is clothed 

 with a fine thick silky fur of a yellowish-gray 

 colour, which is darker on the back than 

 underneath, and is somewhat shaded round 

 the eyes and mouth. The muzzle is that of 

 a rodent, the upper lip is cleft in the middle, 

 the eyes are small and prominent, the ears 

 rounded, almost concealed under the hair. 

 The weak and short feet have four toes in 

 front and three behind, and these toes are 

 united down to their extremities by skin and 

 are covered with small slightly arched hoofs, 

 with the exception of the inner toe of the 

 hind-foot, which carries a small claw. The 

 sole of the foot is covered with a firm, rough 

 naked skin divided into several lobes by 

 means of deep furrows. The Hyracida can 

 make use of these little cushions and furrows 

 for the production of vacuums which act as 

 suckers. In this manner they cling to the 

 smooth surfaces of the rocks, in the clefts of 

 which they have their retreats. They climb 

 just as easily as geckos, and attach them- 

 selves like tree-frogs to smooth surfaces. 



What is most striking in the skeleton of 

 these little animals is the very large number 

 of dorsal and lumbar vertebrae, the fused tail 

 vertebrae, the structure of the feet, which 

 resemble those of tapirs on a small scale, the 

 remarkable width of the skull between the 

 eyes, and the great height and breadth of 

 the posterior half of the lower jaw. 



The dentition is distinguished by an ap- 

 proximation to that of the rodents, indicated 

 mainly, indeed, in the incisors, but made still 

 more marked by the entire absence of canines 

 in both jaws. The development of a large 

 rootless curved incisor in each half of the 

 premaxilla reminds us of the rodents. But 

 these incisors present, not one, but two 

 external surfaces covered with white enamel, 

 while the internal surface is merely formed 

 of dentine. A transverse section of one of 

 these continuously growing incisors exhibits 

 the form of an equilateral triangle, and as the 

 tooth gets worn away by use it always shows 

 two cutting edges, which unite in the middle 

 in a point corresponding to the angle at 

 which the enamel surfaces meet one another. 

 In the milk dentition there is a second pair 

 of quite small incisors, which are soon shed 

 and are never replaced. The lower incisors 

 are four in number, and are very closely set 

 at the fused symphysis of the halves of 

 the lower jaw. They have the form of long 

 compressed blades lying obliquely and worn 

 away transversely. 



Behind the incisors there follows a 

 diastema in place of the canine, and after- 

 wards there follow seven, or even eight, 

 cheek-teeth in each half of the jaw, and these, 

 while all very similar in form, increase in size 

 from before backwards. There are, in fact, 

 four premolars and three or four true molars. 

 The upper cheek-teeth are larger than the 

 lower; both above and below each tooth 

 seems to consist of two halves. In the upper 

 jaw each half has an internal heel surrounded 

 by a strip of enamel, and both heels are 

 united by a strong external serrated enamel 



