\ 



Digestive Sy stein General. 63 



8ome teeth which grow perpetually during the life of the 

 owner ; such teeth require their base to be kept widely ex- 

 cavated for the Persistent pulp* and have therefore neither 

 Neck nor Fang. In most Mammalia particular teeth have 

 special forms for special uses : Incisors for cutting and scrap- 

 ing ; Canines for holding and tearing ; and Molars for 

 grinding ; but the Deciduous and Permanent representatives 

 of each series differ slightly inter se : thus the Permanent 

 Incisors and Caninesf differ from their Deciduous predecessors 

 in size ; and the Permanent Premolars which succeed the 

 Deciduous Molars have generally less complex Crowns than 

 their predecessors. The Molars, properly so called (i.e., those 

 posterior teeth which have no deciduous predecessors), are 

 usually the most complex in their form. Similarity of form 

 is characteristic of the teeth of Monophyodonts. The modi- 

 fications of the crown of the Molar teeth are those that are most 

 intimately related to the kind of food of the species possessing 

 them. Thus in the purely flesh-eating Mammalia the princi- 

 pal Molars are simple, trenchant, and play upon each other 

 like scissor blades : in those species that break bones the 

 Molars have conical Crowns : in the mixed feeding species, the 

 working surface becomes broader and more tuberciilated ; and 

 in the insectivorous species it is bristled with, sharp points: 

 in those that eat shell-fish the Molars are small and obtuse ; 

 and in the partly herbivorous species, the flat grinding surface 

 of the teeth is compKcated hj folds and ridges of Enamel 

 entering the substance of the tooth. When teeth are in ex- 

 cessive number they are generally small, equal, or sub-equal, 

 and of a simple conical form. 



The cavity which is bounded anteriorly by the soft Palate, 

 and precedes the commencement of the alimentary canal 

 (or gullet), viz.y the Pharynx, is generally funnel- shaped, 



* Cf. Eodentia, Proboacidia. In-Enamellata, 

 t Cf. Supra. Situation. 



