CHAPTER XX. 



The Ungulates, or Hoofed Mammals, — Order Ungulata. 



The Hollow-Horned Ruminants. 



Family BoviD^. 



If we except the bats, in which the outermost fingers of the wings are clawless, 

 and some of the seals and their allies, the whole of the Mammals described in 

 the preceding chapters are characterised by having the digits of both the fore 

 and hind-limbs provided either with claws or with thin nails. Moreover, in the 

 greater number of instances, the fore-limbs themselves are endowed to a larger 

 or smaller degree with the power of free movement in several directions ; these 

 movements being displayed to the fullest degree among the Primates, where the 

 hand can be rotated upon the fore-arm, although they are also well-developed in 

 the Cat family. Then, again, the number of digits in the great majority of these 

 animals is five on either one or both pairs of limbs, and in no instance is it less than 

 four. Further, the crowns of their cheek-teeth are never complicated by vertical 

 and lateral infoldings of the enamel, so as to produce when worn down an elaborate 

 pattern. 



The Ungulate, or Hoofed Mammals, such as cattle, deer, camels, swine, horses, 

 tapirs, rhinoceroses, and elephants, of which we have now to treat, differ in many 

 important respects from the above. Thus, while no existing member of the order 

 has the feet provided with claws, in the great majority of cases the toes are 

 enclosed in solid hoofs, although in a few instances they are furnished with broad 

 and flat nails. Then, again, the movements of the fore-limbs are mainly or entirely 

 restricted to a backwards-and-forwards motion, and in no case can the fore-foot 

 be rotated on the fore-leg. Many extinct forms had five or four functional and 

 well-developed digits to the limbs, but in all living members of the order, except 

 the elephants, there are never more than four functional digits ; and in a large 

 number of instances these functional digits are reduced to two, or more rarely 

 three in number. Some species, like the giraffe, have, indeed, but two digits to 

 each foot, while in the horse and its living allies only a single digit remains. 



Feet of It must not, however, be assumed from the last sentence that the 



Ungulates. t oes are gradually reduced from three to two, and from two to one ; 

 the fact really being that the reduction takes place along two different lines, in one 

 of which the number is diminished from four to two, and in the other from three 

 to one. As it is of primary importance, in order to understand the relationship of 

 existing Ungulates to one another, to have a clear idea of the manner in which this 

 reduction of the digits takes place, the subject may be dealt with in some detail. 



