148 MICROSCOPIC ANATOMY OF THE TEETH 



entirely disappeared, and their place is taken by a definite 

 secreting structure. 



He describes and figures capillary loops alternating with 

 epithelial papillae, and in fig. 15 in the illustrations to his 

 paper shows these ' secreting papillae ' pulled away from 

 the capillary loops, and it is very evident that the vessels 

 dip in between the papillse. 



Fig. 76, from a photograph of the enamel and enamel 

 organ of the rat, from a specimen of the author's prepared 

 by the Weil process, also shows these papillae and blood- 

 vessels. 



The same author also describes these papillae as being in 

 intimate relation with the ameloblast cells beneath them, 

 ' each ameloblast seeming to have a root-like process which 

 extends into and is lost in the substance of the papilla to 

 which it belongs '. 



It would be evident, however, that if this is the case, the 

 outer ameloblastic membrane separating the cells of the 

 internal epithelium from those of the stratum intermedium 

 must have either disappeared, or it must be perforated by 

 * the root-like processes of the ameloblasts '. That such 

 processes do- pass through this separating layer between 

 the stratum intermedium and the ameloblasts is, we think, 

 evident in many preparations. 



The present author, in his investigations on enamel develop- 

 ment in certain fish, found and figured a similar condition 

 in the enamel organ of one of the Lr.bridse (Pseudolabrus 

 japonicus), and, as shown in the paper on the subject (16 d), 

 in these fish the whole of the enamel organ appears to be 

 converted into a secreting structure, there being no trace of 

 the cells of the internal or external epithelium, unless the 

 cells within the secreting papillae represent some constituent 

 of the enamel organ of mammalia. 



Leon Williams was unable to detect this definite arrange- 

 ment in other mammalian enamel organs, but only in the 

 Rodents, although in the sheep he found the cells of the 

 stratum intermedium show a more or less orderly arrange- 

 ment around capillary loops. 



In some specimens of the enamel organ of Macropus the 

 cells of the stratum intermedium are seen to have lost their 



