AKTIODACTYLA. 685 



Fam. 6. Caenotheriidae.* Small animals with selenodout dentition, 

 with 4 complete digits, outer digits not reaching gromid, radius and ulna 

 separate ; they are supposed to show affinities to the Tylopoda ; Miocene, 

 France. Caenotherimn Brav., Plesiomeryx Gervais. Dichobune Cuv., 

 U. Eocene, Europe, with tubercular molars is allied here. 



Fam. 7. Xiphodontidae.f With selenodont molars, feet slender, 

 didactyle, the lateral metacarpals and metatarsals much reduced, reduction 

 inadaptive. Teeth continuous, without gap, canine not enlarged ; last 

 premolars hke the molars ; appear to be related to the Traguhdae and 

 Cer\idae, U. Eocene, Europe. Xiphodon Cuv., Dichodon Ow., Amphi- 

 meryx Pomel. 



Fam. 8 Oreodontidae.{ Teeth in closed series or with diastema, 

 molars selenodont, u. molars with 4 rarely with 5 crescents, lower canine 

 incisor-like, and anterior premolar assuming its function ; metacarpals 

 and metatarsals separate. Feet tetradactyle, manus sometimes penta- 

 dactyle. U. Eocene to L. Pliocene of N. America. They are closely 

 allied to the Anthracotheriidae and Anoplotheriidae, but not to any 

 living forms. Protoreodon Scott and Osb., Oreodon Leidy, dentition 

 complete, without diastema, orbit complete, odontoid spoutshaped, said 

 to have had a clavicle. Agriochoerus Leidy, premaxillae toothless, 

 diastema in both jaws, manus A^-ith 5, pes with 4 digits, apparently 

 ending in claws,§ poUex, which is small and functionless, apparently 

 occupies an opposable position. 



Ruminantia.ll 



Living selenodont Artiodactyls with complicated stomach ; usually with- 

 out incisors in the upper jaw, or with only one pair ; tliree pairs of incisors 

 in lower jaw with an incisiform canine applied to thein ; p f m f ; meta- 

 podia 3 and 4 always united to a cannon bone (metacarpals remain long 

 separate in Hyoinoschus). Digits 2 and 5 always reduced and frequently 

 absent ; horns provided with a bony core generally present. The 

 stomach of a typical ruminant (Fig. 306) is divided into four chambers, of 

 which two — the rumen and reticuhun — may be regarded as belonging to 

 the cardiac, and two — the psalterium and abomasum — to the pj^loric 

 division. The rumen or paunch is a large sac on the cardiac side with a 

 papillated lining. It opens by a wide aperture into the smaller reticulum 

 the lining of which is raised into a number of folds which bound small 

 hexagonal cells. The reticvilum opens into the psalterium which is part 

 of the pyloric division ; it is tubular and its lining is produced into a number 

 of longitudinal lammelliform folds, wliich bear some resemblance to the 

 leaves of a book (hence the name). The fovirth chamber is the abomasum 

 or rennet-stomach ; it has a vascular glandular hning and is the digestive 

 chamber of the stomach. The oesophagus opens at the junction of the 

 paunch and the reticulum and there is a groove boimded by muscular 



* Filhol, Ann. Set. GeoL, 8, 1877 and 10, 1879. Owen, Palaeontology, 

 1860. Lydekker, Cat. of the Fofis. Mam. in the B.M. 1885-7. 



t Cuvier, Ossem. Foss., 3, 1812. 



X Scott, Morph. Jahrb., 16, 1890, p. 319. 



§ Wortman, Bidl. Amer. Mus. N. Hist , 7, 1895, p. 145. In spite of 

 tliis remarkable feature, the animal appears to have been digitigrade. 



II Rutime\er, Fauna der PjahlbauUn. Id., Versuch einer naturlichen 

 Geschichte des Rindes, D nlcseh. der Schweizer Nattirf. Oesellschajt, 22 

 and 23. Suadevall Metlodische Ubers. iib. d. tmederkauenden Thicre, 2 

 Theale, 1847. 



