MAMMALIA. 515 



mastication or rumination is effected by the molar teeth. 

 The chewed food is then passed down to the psalterium 

 and the abomasum where digestion commences. The 

 horse, on the other hand, masticates his food at the time 

 of feeding, and there is in this case no rumination or 

 "chewing the cud." The rest of the alimentary canal is 

 very similar in both types, the caecum being large and 

 the intestine long, characters usually found in herbivorous 

 animals. 



Returning to the rest of the skeleton we find that the 

 vertebral column is of the same general type, the cervical 

 vertebrae especially being markedly opisthocoelous. The axis 

 vertebra has a crescentic odontoid process, another feature 

 in which the horse and the ox converge, though the more 

 primitive forms of each sub-order differ in having simple 

 conical odontoid processes. 



The dorso-lumbar vertebrae are nineteen in number in 

 the ox, but huenty-three in the horse. In a similar manner 

 the ox has usually twelve to fifteen pairs of ribs, whilst the 

 horse has from eighteen to nineteen pairs. The ribs of the 

 ox are usually flatter and broader. In both types the front 

 dorsal vertebrae bear very long neural spines, to which is 

 attached the elastic ligament {ligamentum nuchce) running 

 forward along the cervical vertebrae to the skull and sup- 

 porting the weight of the head. 



The difference in the number of dorso-lumbar vertebrae 

 is probably due to the shifting of the pelvis further forward 

 in the ox than in the horse, in its turn connected with the 

 greater proportionate " pushing " power of the ox. 



Now let us turn to the limbs and limb-girdles. In both 

 the same plan prevails. The scapula is elongated and 

 narrow, of the cursorial type, and the clavicle is absent ; it 

 is not required in animals in which the Hmbs are not moved 

 inwards to the middle line and would indeed be a source of 

 danger when, as in jumping, the weight of the body is 

 thrown on to the fore-limb. The pelvis is of the same 

 general type in each, with large ilia fusing not only with the 

 primitive sacral vertebrae, but with three or four others in 

 addition. The limbs have in the cursorial type to perform 

 a great uniformity of movement, and by reduction and 

 fusion from the pentadactyle type they approximate to the 



