228 NOTOUNGULATA order viii 



correlated with the size of body. On the whole, however, they are more 

 nearly comparable with those of carnivores and rodents than with those of 

 true ungulates. The long tibia of small forms is slender, the humerus has 

 an entepicondylar foramen, and the femur a third trochanter. The ulna is 

 very massive and is not fused with the radius. These are frequently crossed. 



Fig. 310. 



Protypotherium ausirah Ameghino. Upper molar, from inside (a), behind (ft), and outside (c). 



Lower molar, from inside (d), outside (e), and behind (/). i/i- 



All of the carpals are free and alternately arranged. The astragalus 

 always has a convex nearly hemispherical navicular facet; and the fibula, 

 usually not fused with the tibia, always articulates with the calcaneum. 

 The number of metapodials varies between three and five ; the median keel of 

 their distal articulation is always restricted to the posterior surface. The 

 terminal phalanges are at times claw-like, although slightly flattened in 

 front, or in other cases broad hoofs, or hooked, deeply fissured claws. 



The Nofonngulafa are divided into five suborders as follows : Typotheria, 

 Toxodontia, Entelonychia, Astrapotherioidea and Pyrotheria. 



Suborder A. TYPOTHERIA Zittel.i 



Extinct plantigrade or digitigrade herbivores Visually vnth four-toed manns and 

 pes. Dentition, as a rule, is complete, the inner, upper incisors enlarged, the outer 

 incisors and canines often reduced, or all the teeth graduating one into another and 

 in a compact row. Upper molars are lophodont, lower ones selenolophodont. In the 

 beginning these were brachyodont and rooted, later they become hypsodont, prismatic 

 and without roots. Clavicle often present. Carpals alternating, centrale lacking. 

 Humerus tvith entepicondylar foramen. Femur with third trochanter. 



The Typofheria are restricted to the Tertiary and Pleistocene of South 

 America. They are very closely related to the Toxodontia, and resemble in 

 external appearance many rodents and the Hyracoidea, though this resemblance 

 depends merel)'' on convergence and not on true relationship. 



The skull is like that of rodents in that it is elongated and has a straight 

 transverse suture separating the frontals from the parietals. The forwardly 

 directed nostrils are bounded on the side by the high premaxillary bones, 

 and above by the long nasals reaching to the extremity of the rostrum. 

 The parietals have a small sagittal crest. The zygomatic arch, which is very 

 strongly developed posteriorly, is very high, and the wide orbits are frequently 

 bounded posteriorly by a processus postorbitalis of the frontals. The infra- 

 orbital foramen lies in front of the zygomatic arch. The broad occiput has 

 a supraoccipital crest and a long paroccipital process. The broadening and 



1 Gervais, P., Remarques sur le Typotherium. Zool. et Paleont. Generales, vol. i., 1867-69. — . 

 Sinclair, W. J., Report of the Princeton University Expedition to Patagonia, vol. vi. . part I. 

 1909. 



i 



