MASTICATION. ; 



of lime in its composition amounts to -^ths. The cortical 

 substance or cement scarcely exists in the human teeth ; hut 

 in the teeth of oxen, in which it abounds, it furnishes, by 

 chemical analysis, 42 per 100 of organic matter, 50 per 100 

 of phosphate of lime, and 4 per 100 of carbonate of lime. 



In the ivory of the teeth of man we discover, by means 

 of the microscope, a multitude offlexuous branching tubes of 

 extreme tenuity (called Haversian canals), which open or 

 terminate in the central cavity: these tubes contain calcareous 

 matter ; they run towards the surface of the tooth, and their 

 divisions terminate frequently in little cavities bearing a close 

 resemblance to the little cells found in the ordinary osseous 

 tissue. The enamel, examined under the microscope, exhibits 

 a multitude of fibres, or rather hexagonal prisms, in appear- 

 ance crystalline, closely pressed against each other, and 

 directed perpendicularly towards the surface of the tooth. 

 Finally, the cortical substance is characterized by the pre- 

 sence of a great number of osseous cellules, and of irregular 

 calciferous tubes. These tissues are not all met with in the 

 teeth of all animals; the enamel and cortical substance are fre- 

 quently absent in fishes: and occasionally the dentine, instead 

 of containing a single medullary cavity, contains several. 

 51. The teeth, in some animals, instead of being 



Fig. 16. Osseous Head of the Whale,* 

 with the Whalebone present. 



contained or fixed in the alveolar cavities (sockets), - 

 -unite by their base with the jawbone or maxilla, 

 becoming, as it were, a part of it : this happens 

 in many fishes, and occasionally the teeth, instead 

 of resembling bones, offer merely the consistence 

 of horn. Finally, in the whalebone whale (Fig. whale- 

 16) the teeth seem to be replaced by large flexible bone, 

 plates of whalebone (fanons, Fig. 15); and in other ( Fanon ^ 



* Mysticetus; Greenland Whale, or Whale of Commerce. Kudimentary 

 teeth exist in the ioetus of the whale in both jaws. R. K. 



