SUBORDER A 



CONDYLARTHRA 



119 



The low, elongate skull is but slightly specialised and combines 

 characters of the creodonts and primitive perissodactyls and artiodactyls. 

 The orbits are wide open posteriorly, the profile outline of the skull is 

 almost horizontal, the cranium has a sagittal crest, the brain is very small 

 and the cerebellum lies behind the smooth hemispheres of the cerebrum. 

 The postglenoid process is very well developed, and the dentition is 

 complete. The incisors and canines are like those of the creodonts and the 

 primitive perissodactyls and artiodactyls. The P are much simpler than the 

 brachyodont, three or four rooted tritubercular or quadritubercular molars. 



The dental formula is complete ; the last milk cheek teeth are similar 

 to the first molar. The upper M have two outer, usually one inner, and 

 two middle cusps. The lower M have four primary cusps and one or two 

 secondary cusps. 



The plantigrade or semidigitigrade extremities (Fig. 148) have five toes 

 in the manus and pes, of which the three inner digits are more strongly 

 developed than the two outer ones. 

 The clavicle is usually present. The 

 humerus has always an entepicondylar 

 foramen, and the femur a third tro- 

 chanter. Radius and ulna, as well as 

 tibia and fibula, remain distinct. The 

 fibula ends, as in carnivores, without 

 calcaneal articulation. The two rows 

 of carpals are almost serially arranged 

 in Phenacochis, the centrale absent ; in 

 other Condylarfhra the carpals are alter- 

 nating and an os centrale is present. 

 The tarsus is essentially the same as in 

 the creodonts. The concave articular 

 surface of the astragalus extends rather 

 far down on the navicular and touches 

 the cuboid only on the lateral surface. 

 The trochlea often has a perforation, 

 the " astragalar foramen." The ter- 

 minal phalanges are distally flattened, 

 but are pointed and quite often bifid, 

 as in the case of the creodonts. 



In external appearance, the Con- 

 dylarthra doubtless resembled the 

 omnivorous carnivores rather than the 

 ungulates. The character of the articu- 

 lations in the manus and pes did not permit very swift movement, while the 

 dentition suggests subsistence on both vegetable and animal food. The largest 

 forms attained the dimensions of the wolf ; the smallest those of the rabbit. 



Fig. 148. 

 Hyracops socialis Marsh. Lower Eocene 

 Wasatch, Wyoming. A, Left .fore-foot. B, Left 

 hind-foot. 'U. (Alter Marsh.) R, Radius ; U, 

 ulna; a, astragalus; ca, calcaneum ; cb, cuboid; 

 ce, centrale ; c^"^ cuneiforms ; I, lunar ; m, 

 magnum ; n, navicular ; p, pisiform ; .<, scaphoid ; 

 td, trapezoid ; tm, trapezium ; u, unciform ; x, 

 epicuneiforra. 



Family 1. Mioclaenidae Osborn and Earle. 



Upper molars suUriangular, broader than long, without a second internal cusp ; 

 lower molars usually quinquetubercular, the anterior cusp (paraconid), however, if 

 present, very small. Premolars simple, the second and third only with internal 



