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Wf/'Jh'fCAX MCShlWf crihK LEAFLETS 



Patagonia and singularly like the horse in many ways. These animals 

 likewise lost the lateral toes one after another, and concentrated the 

 st(»|) on the central toe; they also changed the form of the joint-surfaces 

 from ball-and-socket to pulley-wheel joints; they also lengthened the 

 limhs and the neck; and they also lengthened the teeth, and complicated 

 their pattern. Tnlike the true horse, they did not form cement on the 

 tooth, so that it was by no means so efficient a grinder. This group of 

 animals native to South Ameiica became totally extinct, and were suc- 

 ceeded by the horses, immigiants from North America, which in their 

 turn became extinct befoic the appearance of civilized man. 



Many of the contempoi'aries of the horse in the northei-n hemi- 

 sphere were likewise lengthening the limbs, lightening and strengthening 



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FIG. 23. ONE-TOED PSEUDO-HORSE 



Fore and hiiul foot, one-half natural size. The Thoathcrium has gone even further 

 than the modern horse in reducing the side toes to tiny rudiments instead of splints. 

 The skull and teeth show the animal to be closely related to Diadiaphorus (Fig. 22) 

 and widely different from true horses. Thoathcrium was a little larger than a fox 

 terrier and lived in South Americ^i during the Miocene Epoch. From .specimens 

 in tlie Princeton Muscmmu and the .Kmerican Museum of Natural Historv 



