DENTAL TISSUES. 



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A third kind of complication is pr(xliiced by an aggregation of 

 many simple teeth into a single mass, fig. 247. 



The examjjlcs of these 

 truly compound teeth are 

 most common in the class 

 of Fishes, but the illustra- 

 tion here selected is from 

 the Mammalian class. 

 Each tooth of the Cape 

 Ant-cater ( Orifcteropus) 

 presents a simple form, is 

 deeply set in the jaw, 

 but without dividing into 

 fangs ; its broad and flat 

 base is porous, like the 

 section of a common cane. 

 The canals to which these 

 jiores lead contain pro- 

 cesses of a vascular pulp, 

 and are the centres of ra- 

 diation of as many independent series of dentinal tulniles. Each 

 tooth consists of a congeries of long and slender prismatic 

 columns of dentine, cemented together by their ossified ca])sules. 

 Fig. 247 is part of a transverse secti(.)n of such compound tooth, 

 showing c the cement, d the dentine, p the 

 pidji-cavity of the denticles, and d' a section 

 of one of the denticles just Ijeyond its bifur- 

 cation. 



In the series of tissues, ' cement ' and 

 ' dentine,' under its diverse modifications, 

 rank with osteine. Enamel is a tissue per 

 se : it might he compared to calcified cpi- 

 derm ; but, in the teeth of Fishes, there are 

 intermediate gradations of structure which 

 link enamel to dentine, and this to bone. 



The general form of the matrix or forma- sul i 



tive organ of teeth, and the relative position of the dentinal pulp 

 to its product, liear a close resemldance to tlic foimative organ 

 of hair and bristle. In these, however, the papilla or pulp is 

 de^'eloped from the skin, in teeth from the mucous membrane. 



Teeth further agree with the extravascular appendages of the 

 skin in being shed and reproduced, sometimes once, sometimes 

 frequently, during the lifetime of the individual. In some 



245 



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