T6 ON THE HOMOLOGIES AND ORIGIN OF THE 



Anioebodont. 



( Palceotkeriodont. 



Symborodont. i ^ y 7 . 



( Symoorodont. 



Hippodont. Selenodont pt. 



f Bathmodont, 



Loxolophodont. { ^ , i i , 



{ Loxolophodont. 



The characteristics of these groups are as follows : — 



A. Antiodonts. 

 Selenodonts. 



Constructed, typically, like the upper molars. Ruminantia. 



Hyracodonts. 



External tubercles compressed longitudinally and crescentic in section, continu- 

 ous by a cross crest with the corresponding tubercle of the inner side. 



The animals which possess this type of teeth are the Rhlnocerus, Hyracodon, 

 and the Hyrax ; it is nearly approached by some of the Hyrachyi. It corresponds 

 in structure with the true tapirodont arrangement of the maxillary teeth; but 

 many of the Tapirodonts have the Trichecodont type of mandibular teeth. 



Trichecodonts. - 



Definition the same as for the maxillary teeth. 



Tapirus, Lophiodon, Hyrachyus, Dinotherium, Elephas, Trichecus (the manati), 

 and the Kangaroos and their extinct allies belong here. 



B. Amcebodonts. 

 Hippodonts. 



In the horses the maxillary molars are constructed on an opposite crested basis, 

 while the mandibulars represent an alternate crested type. This is not constituted 

 as in the next form, by a union of alternating tubercles, but as in the Selenodonts 

 by the special development of each crest into a crescent extended antero-posteriorly. 

 As alternating, the inner crescents stand at the apices of the outer, and are con- 

 nected with them. In Anchitkerium the inner are so reduced as to constitute a 

 condition intermediate between the Hippodont and Symborodont types. 



Symhorodonts. 

 The alternating tubercles connecting by obUque ridges which form together 



two Vs. 



To this type is to be referred a great number of Perissodactyles, e. g., Anchitke- 

 rium, PalcBOtherium, Palmosyops, Titanotherium, Symborodon, Anchippodas. 



