MOLAR TEETH OF THE MAMMALIA EDUCABILIA. 249 



2. The Mandibular Teeth. 



The h'pes of structure are less numerous tban those of the 

 maxillary teeth, since I am only acquainted with six. Still more 

 distinctly than those of the upper jaw do they represent the types 

 of opposite or alternating tubercles, or the antiodont and amoebo- 

 dont. The essential principles of modification are the same as in 

 the maxillaries, and they correspond with them as to genera, as 

 follows : 



Antiodont. 



Inferior. 



Selenodont. 

 Hyracodont. 



Trichecodont. 



Superior. 



Selenodont. 



Tapirodont pt. 

 j Tapirodont pt. 

 ] Trichecodont. 



Symborodont. 



Hippodont. 



Loxolophodont. 



Amcebodont. 



J Palfeotheriodont. 

 ( Symborodont. 

 Selenodont pt. 

 j Bathmodont. 

 ( 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, continuous by a cross-crest with the cor- 

 responding tubercle of the inner side. 



The animals which possess this type of teeth are the Rhinoce- 

 rus, ffyracodon, and the Hyrax ; it is nearly approached by some 

 of the Hyrachyi. It corresponds in structure with the true tapiro- 

 dont arrangement of the maxillary teeth ; but many of the Tapiro- 

 donts have the Trichecodont type of mandibular teeth. 



Trichecodonts. — Definition the same as for the maxillary teeth. 



Tapirus, Lophiodon, Hyrachyus, Dmotherium, Elephas, Tri- 

 checus (the manati), and the Kangaroos and their extinct allies 



belong here. 



B. Amcebodonts. 



Hippodonts. — In the horses the maxillary molars are con- 

 structed on an oj)posite crested basis, while the mandibulars repre- 



