DEVELOPMENT OF THE ENAMEL 129 



stages of enamel formation, the external epithelium lies in 

 close contact with the stratum intermedium, and the blood- 

 vessels of the capsule are in close proximity to its cells. It 

 is contended by Leon Williams (30) that in the rat the 

 blood-vessels enter the stratum intermedium, and that their 

 loops dip into the spaces between the cells, from which they 

 can be pulled away, the vessels then projecting as long 

 processes, and he claims for the stratum intermedium the 

 functions of a true secreting organ in this animal. 



FIG. 75. The enamel organ of Macropus at the commencement of 

 calcification, st. Stellate reticulum ; s. stratum intermedium ; a. amelo- 

 blasts; od. odontogenic zone ; o. odontoblasts. On the left calcification 

 of the dentine has just commenced and the outer ameloblastic membrane 

 appears, but is not seen on the right side where there is no calcification. 

 x400.) 



Certainly the photographs accompanying his description 

 give every evidence of such an arrangement, and the con- 

 ditions found in certain fish in which blood-vessels or sinuses 

 form a conspicuous part of the enamel organ, as shown by 

 the author in a recent paper, would tend to confirm this 

 observation. Fig. 76, from a photograph of a preparation 

 by the author, shows these papillae and loops in the enamel 

 organ of the rat. 



The Internal Epithelium. Ameloblast or Adamantoblast 



