396 CLASSIFICATION OF VERTEBRATES. 



The TITANOTHERIID^E of the eocene and miocene of Europe and America 

 were mostly large animals with toes four and three on the fore and hind feet 

 respectively, and the teeth varying between * to f , c |, p f to , m f . 

 Pal&osyops (Lymnohyus} . Titanotheriuin {Brontotherium) has a pair of 

 large bony processes on the snout, probably covered with horns. One spe- 

 cies nearly as large as an elephant. 



The position of the CHALICOTHERIID.E is uncertain. In the teeth it is 

 distinctly perissodactyl, but its three-toed feet were plantigrade, and termi- 

 nated with long, curved claws. The family ranges from the eocene to the 

 pliocene, and is best developed in Europe. Moropus, Macrotheriuw. 



SUB-ORDER 3. ARTIODACTYLA. 



Unguligrade or digitigrade ungulates in which the toes are symmetrically 

 developed about an axis passing between the third and fourth digits. Fre- 

 quently a reduction from the full dentition of 44 teeth : premolars unlike the 

 imolars, the former with one lobe, the latter with two, except the last, which 

 has three lobes ; femur without third trochanter ; fibula articulating with the 

 calcaneum. Stomach complex ; caecum often present, large and convoluted ; 

 mammae 2 or 4, inguinal ; placenta diffuse or cotyledonary. 



The artiodactyls are mostly large animals, distributed all over the earth, 

 with the exception of the Australian region. The relations of the axis of the 

 foot produce the well-known cloven hoof so characteristic of the group, while 

 in many there is a tendency towards the loss of the incisors and canines in the 

 supper jaw. Another common feature is the development of bony horn cores 

 jupon the frontal bones. The recent forms are frequently sub-divided into 

 four series, Suina, Tragulina, Tylopoda, and Ruminantia (Pecora, or Cotv- 

 lophora), but when the extinct species are taken into account, the divisions 

 break down. For convenience the characters of these groups may be given 

 liere. 



Suina : with the families Hippopotamidae and Suidae, with bunodont 

 molars and distinct or but partially fused third and fourth metatarsals 

 and metacarpals; i.e., without a cannon bone. Tragulina: with the family 

 Tragulidae, in which a cannon bone usually occurs ; and the stomach is three- 

 chambered, the manyplies being absent ; fibula complete. Tylopoda : includ- 

 ing the Camelidae : with only digits 3 and 4 developed, their metapodials 

 fused above ; manyplies absent, red blood corpuscles oval. Ruminantia : with 

 the families Cervicornia and Cavicornia. In these there are no upper inci- 

 i) sors; a cannon bone is present, the stomach four-chambered, and the pla- 

 centa cotyledonary. The processes concerned in rumination may be described 

 ihere, although a chewing of the cud occurs also in the camels. When feed- 

 ing, the food as swallowed passes into the paunch, and thence to the honey- 

 -comb. In both of these it is softened, and then is regurgitated into the 

 mouth, and masticated by the teeth. After this comminution it is swallowed 

 again, but at this time it passes directly to the third stomach, or manyplies, 

 and thence to the abomasum, which is the true digestive stomach. 



The central stem of the artiodactyls seems to be the PANTOLESTID/E of 

 the American eocene, with bunodont molars, and probably four-toed feet. 



