CLASSIFICATION OF ANIMAL PKEPAEATIONS. 



427 



portions of the ethmoid bone wUl often require no prepara- 

 tion, being sufficiently transparent for all purposes of exami- 

 nation. 



Besides the above described specimens of recent bones, 

 there are others found in the fossil state that, when cut and 

 poHshed, will exhibit their intimate structiure as well as the 

 fresh specimens; they are generally prepared in the same 

 manner as the fossil woods before noticed ; others, when very 

 opaque, may be entirely mounted in balsam. The subjoined 

 list wiU afford the names of a few animals in which the most 

 interesting structures may be found : — 



Teeth. — Like bone, these require to be made thin and 

 polished, in the manner described at page 329; but the 

 operation is very difficult, as the majority of teeth are sup- 

 plied with a coating of enamel of ffinty hardness. As there 

 are three distinct elements, viz., the cement, the ivory, and 

 the enamel entering into the formation of most teeth, it wiU 

 be necessary that the sections be made in many directions, in 

 order to arrive at a true knowledge of the formation of each. 

 In the following list will be given the names of a few of the 

 animals whose teeth exhibit some well-marked points of 

 structure : — 



