694 MAMMALIA [CH. 



of these the food is completely filtered from all the solid matter it 

 contains. It then passes on into the fourth and last compartment, 

 the ab omasum, whose walls are raised into but a few ridges and 

 which is lined with an epithelium containing numerous gastric 

 glands. This leads into the duodenum or first part of the intestine, 

 in which the digestion is completed. The teeth of the Ruminants 

 have no distinct tubercles like those of the Pig, since these pro- 

 jections have become confluent so as to form hard curved ridges of 

 enamel; and as the jaws shift on each other sideways, the upper 

 and lower back teeth produce a grinding action just as two mill- 

 stones do. The name SELENODONTIA (Gr. o-cXywj, the moon) has 

 been given to the Ruminantia on account of the crescentic ridges 

 on their teeth, which are termed selenodont. It is interesting to 

 note as evidence of the more advanced structure of the Ruminantia 

 as compared with the Suinae, that the selenodont teeth always pass 

 through a bunodont stage in their development. The canines in 

 the upper jaw are long in the male Moschus, who no doubt uses 

 them in his fight for the possession of the female. The lower 

 canines however are usually placed close to the lower front teeth 

 and are indistinguishable from them. There are with few ex- 

 ceptions no front teeth in the upper jaw, and the grass is bitten 

 off by pressing the lower front teeth against a patch of hardened 

 gum. 



The feet of the Ruminants are organs beautifully formed for quick 

 motion ; the ideal which Nature has so to speak striven to attain 

 being the same in their case as in that of the Horse, though she 

 has had to start from a different basis. As in the case of the Horse, 

 the end in view has been a firm jointed lever moving only in one 

 plane; but in Ruminantia this has been attained by keeping two 

 fingers and two toes and so to speak glueing them together except 

 in the bones of the hoof. Ruminants, like Horses, walk on the 

 points of their finger- and toe-nails; the metacarpals of the third 

 and fourth digits are fused together, while of the outer fingers and 

 toes only vestiges remain which hardly ever reach the ground, and 

 often do not appear externally. The "cloven hoof" is therefore 

 formed by the nails of two fingers or two toes (Fig. 347). 



The families composing the division Ruminantia are the TRAGU- 



LIDAE or Chevrotains ; the CAMELIDAE or Camels 



(Tylopoda); the CERVIDAE or Deer; the GIRAFFIDAE 



or Giraffes; the ANTILOCAPRIDAE which has but one species, 



the Prong-buck, Antilocapra americana; and the BOVIDAE or 



