160 UNGULATES. 



of the crescents turned outwardly. In the lower jaw the molars are narrower, and 

 with a reverse structure ; that is to say, the crescents are on the outer side of the 

 tooth, with their horns turned inwardly. Accordingly the name of crescent-toothed 

 (selenodont) Ungulates is applied to all the ruminating members of the group. 



It is important to observe that the true Ruminants are alone characterised 

 by the whole of the four under-mentioned features, viz. no front teeth in the 

 upper jaw, a four-chambered stomach, complete cannon-bones, and the feet encased 

 in hoofs. Moreover, it is only in the members of this group that horns are ever 

 met with ; these appendages being always arranged as a symmetrical pair (occasion- 

 ally two pairs) on either side of the middle line of the skull. 



Hollow-Honied The hollow-horned Ruminants, or Bovidai, are distinguished from 



Ruminants, their allies by the presence of true horns; that is to say, of hollow 

 and unbranched sheaths of horn growing upon bony protuberances, or cores, arising 

 from the frontal bones of the skull, as shown in the figure on p. 159 ; neither 

 the horny sheaths nor the bony cores being shed at any period of existence. In 

 all existing wild species these homs are present at least in the male sex ; but in 

 many domesticated races of cattle, sheep, and goats, they are absent in both sixes 

 and the same holds good for certain extinct members of the family. Usually the 

 molar teeth of the hollow-horned Ruminants are characterised by the great relative 

 height of their crowns, as shown in the figures of the molar teeth of the nilgai 

 given on p. 155 ; and in all cases there is no tusk or canine tooth in the upper jaw. 

 In some few instances the small lateral toes may be completely absent, but they are 

 generally represented merely by the small spurious hooflets alone, which may be 

 supported internally by minute and irregularly-shaped nodules of bone. 



The hollow-homed Ruminants are chiefly Old World forms, although they are 

 represented in North America by the musk-ox, the American bison, the Rocky 

 Mountain goat, and the bighorn sheep. They are quite unknown in the southern 

 half of the New World. 



The Oxen. 



Genus Bos. 



The oxen include the largest and most massively-formed members of the 

 hollow-horned Ruminants, and comprise not only the animals thus commonly 

 designated, but likewise the bisons, yak, and buffaloes. As a rule, they are large 

 and heavily -built animals, with very short and thick necks, and the massive and 

 relatively short head carried nearly in the line of the back ; the males generally 

 being provided with a large dewlap, l-unning along the throat from the chin to 

 between the fore-legs. The tail is always long, and is generally thinly haired 

 throughout the greater part of its length and tufted at the extremity, but in the 

 yak it is thickly haired throughout. The muzzle is broad, naked, and moist ; and 

 there are never any " tear-pits " or glands below the eye, which are so frequently 

 present in the antelopes; and in consequence of the absence of these tear-pits 

 there are no depressions in the skull immediately below the eyes for their recep- 

 tion. The horns, which are present in both sexes and of nearly equal dimensions 

 in both, may be either cylindrical or more or less markedly angulated ; and are 



