COMPARATIVE ANATOMY OF THE TEETH. 271 



mark of distinction among the different mammalia. They 

 are all received into proper alveolar cavities, supported by 

 and contained within the maxillary or intermaxillary bones. 

 The teeth of mammalia are also distinguished from those 

 of man by their varied conformation, especially of the 

 crown, which is asserted to differ as widely as the food upon 

 which they each respectively subsist Those of the carniv- 

 erous and ferocious class, which feed on flesh for example, 

 have crowns with much stronger prominences, and more 

 pointed and cutting edges, while those on the other hand 

 which live on vegetable food, and are peaceable in their 

 disposition, have flat and large crowns. 



The human teeth come between these two extremes, and 

 partake of the characters of both, and hence it is that man 

 is regarded as an omniverous animal, his teeth being 

 adapted to living on both animal and vegetable diet. 



The teeth of the lower mammalia consist, as in man, of 

 ivory and enamel, and they are arranged in similar man- 

 ner. The animals, however, have a substance called cement, 

 or, as Tenon terms it, the "osseous cortical substance;" 

 which, though existing in human teeth, is by no means so 

 abundant or extensive. 



The cement is harder than the ivory, but not so hard as 

 enamel. It blackens sooner, on exposure to heat, than the 

 latter, showing that it contains a greater amount of animal 

 matter. It is said to be so abundant in the grinders of the 

 elephant, as to form about half their volume. Its mode of 

 formation is not settled : some think it is the ossification 

 of the internal membrane of the follicle others, with Cu- 

 vier, that the same organ which secretes the enamel, after 

 it is formed, then furnishes the cement. The chemical 

 analysis of cement is given as follows : 



Animal matter, 43.01 



Phosphate of lime, 52,94 



Carbonate of lime, 4.05 



The duration or period of growth in the teeth of man and 

 mammalia varies, so much so that in the statement about 



