70 



KANSAS CITY REVIEW OF SCIENCE. 



pec 



zjae 



Fig. 12. Fig. 13. 



Fig. 12 — Left sup. molar of anchitherium Aureliense, nat. size, (after 

 Gaudry). The letters pec and ace should be made to change places. 

 Fig. 13. — Left inferior molar of same, nat. size, (after Gaudry. 



In all the preceding 

 animals, the tibia and 

 fibula are strong and 

 distinct. The ulna and 

 radius are also separate 

 and the humerus pre- 

 sents a single groove 

 for the passage of the 

 tendon of the biceps 

 muscle, which latter fact 

 is likewise true of An- 

 chitherium. But in this 

 animal the fibula be- 

 comes slender and its 

 distal extremity adheres 



closely to the tibia. The ulna is also reduced and shows a tendency to coossifi- 



cation with the radius ; and the skull in its general appearance is decidedly equine. 



The PalceoiheriidcE range as far back as the middle Eocene, 



but the genus Anchitherium has not been found in any 



other strata than the lower and middle Miocene. 



Following close in geologic succession, we meet with 



another genus of this family, which, as we should antici- 

 pate, departs more widely from the primitive ancestral 



type and approaches more closely to the modern horses. 



This is the genus Hippotherium, Kaup. The outer toes 



are so much reduced as to have been practically function - 



less to the animal. The fibula is incomplete in the middle 



portion of its shaft, and its distal extremity is coossified 



with the tibia, while the ulna is firmly anchylosed with 



the radius but is still distinguishable throughout its whole 



extent. The bicipital groove of the humerus is double as 



in the existing horses, and with the teeth resemble those 



of the horses very strongly. The valleys are deepened 



by the lengthening of the cusps and ridges and are filled 



by a thick deposit of cementum. The crowns of the in- 

 cisors also show that peculiar invagination seen in the 



incisors of the horse. The homologies of the various size, (after Gaudry. 



parts of the molars are seen in Fig. 15, a tooth in which the cementum has been 



removed, and the points of the cusps and ridges remain undisturbed by wear. 

 It is noticeable that the four principal lobes ae^ pe, ai a.ndj>i hold about the 



same relation to each other. The cross crests ace and pec have their obliquities 



increased, and the anterior bends around on the inner portion of the face and 



Fig. 14. 



Left fore foot of Auchitker- 

 iutn anreliense, one-fifth nat. 



