TEETH. 



705 



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calcareous matter becomes crowded and consolidated ; as 

 the process advances, the bone thickens, and a series .of 

 grooves, of a stellate form as in the annexed cut (fig. 337, 

 No. 2), are found upon its sur- 

 face, which become gradually 

 converted into canals for the 

 passage of blood-vessels. 



In certain forms of disease, 

 many of the soft parts of the 

 human body are converted into 

 cartilaginous and bony masses, 

 which have received the name 

 of Enchondroma (figs. 338 and 

 339). The microscopical cha- 

 racteristics of this change have 

 been described by the author 

 in the Transactions of the Patho- 

 logical Society of London, vol. iv. 



Teeth. It is desirable to be- 

 come acquainted with the struc- 

 ture of teeth under the micro- 

 scope ; they are highly interest- 

 ing to the physiologist, and im- 

 portant guides to the naturalist 

 in the classification of animals. 

 Professor Owen has said, "If 

 the microscope is essential to 

 the full and true interpretation 

 of the vegetable remains of a 

 former world, it is not less in- 

 dispensable to the investigator 

 of the fossilised parts of animals. 

 It has sometimes happened that 

 a few scattered teeth have been 

 the only indications of animal 

 life throughout an extensive stratum; and when these 

 teeth happened not to be characterised by any well-marked 

 peculiarity of external form, there remained no other 

 test by which their nature could be ascertained than that 

 of the microscopic examination of their intimate tissue. 

 By the microscope alone could the existence of Keuper- 



z z 



Fig. 336. A vertical section oj 

 cartilage, with clusters of cells 

 arranged in columns previous to 

 conversion into lone, which is 

 seen consolidated at the upper 

 surface. The greater opacity of 

 this portion is owing to the in- 

 crease of osseous fibres, the 

 opacity of the cell contents, 

 and the multiplication of oil- 

 globules ; the dark intercel- 

 lular spaces become occupied 

 by vessels. 



