IV. VERTEBRATA: MAMMALIA, UNGULATA 



569 



The molars are selenodont. With few exceptions Ruminants are of large size 

 and many bear horns on the frontal bones, larger in the males and may occur 

 exclusively in that sex. In the giraffes these are cones free from the frontals and 

 covered with skin. In others (Cavicornia) the horn cores fuse secondarily with 

 the frontals and are covered with a sheath of horn. Lastly, the horns are out- 

 growths of the frontal bone, in which usually the outer coats of skin and hair 

 (velvet) are soon lost and only the bone projects freely (antlers). These are 

 shed yearly, the new antler which takes its place being larger and consisting of 

 a larger number of branches or tines, thus constituting an index of age (Cervi- 

 cornia). Camelopardalid^ (Devexa), giraffes, long-legged forms from 

 Africa with persistent horns; teeth f'MI, Giraffa, Okapia. CerviDjE, deer, 

 deciduous horns in the male. Ccrvus,* common deer; Alces* moose; Rangifer* 

 reindeer; Moschid.e, horns lacking, males with enlarged upper canines and a 

 musk gland; Mosclii^s, central Asia. Tr.\gulid.e, primitive, Asia and Africa. 

 The C.A.VICORNLA. include many species, some of great economic importance; 

 teeth ""33. Bovid.e: Bos tati.nis, domestic cattle, probably descended from 

 three distinct stocks {B. primigenius, aurochs, B. longifrons and B. frontosus); 

 Bison/' including B. europeus, bison proper, and B. americamis* our 'buffalo.' 

 Bubalus, the true buffalo of the Old World. Ovid^: Ovis aries, sheep; O. 

 montana* big horn; Capra hircus, goat; Ovihos moschatus* musk ox. Anti- 

 lopid.e: including a host of Old World forms (Anlilope, Gazella, Rupicapra 

 tragus, the chamois, etc.) and Antilocapra americana* prong horn, which sheds 

 its horns, and Hoploceras mnntanus* Rocky mountain sheep. 



Section III. TYLOPOD.\, stomach without manyplies, no frontal horns, 

 diffuse placenta. Caindus, Old World camels; Aucltcnia lama, A. alpaca of 

 South America. 



Paleontology of the Ungulata. 



Abundant paleontological material, especially from the tertiary of our 

 western states, has cleared up many lines of ungulate descent and has shown 

 it probable that the CONDYL.A.RTHR.\ of the eocene, with five-toed planti- 

 grade feet, well-developed ulna and fibula, and omnivorous dentition, formed 

 the stock from which the artiodactyles and perissodactyles descended, and 



Fig. 617. — Evolution of fore foot of horse (from Wiedersheim). i, Orohippus 

 (eocene); 2, Mesohippus (lower miocene); 3, Miahippus (miocene); 4, Prolohippus 

 (upper pliocene) ; 5, Flwhippus (pleistocene) ; 6, Equus. 



possibly carnivores and primates as well, the ungulate line extending through 

 the Amblypoda. From one group of these (Phenacodontid.e) the lines of 

 rhinoceros and tapir have come, and in an almost complete series we know the 

 ancestry of the horse. Hyracotherium (Eohippus) and Orohippus of the eocene 

 had the fore feet four-toed (fig. 617, i) ; Palceolhcrium and Mcsohippus (2) of the 

 lower miocene and Miahippus of the later miocene were three-toed, while Mery- 

 hippus and Hipparion {Pliohippus, 4) of the pliocene were near the horse in 



