HISTOLOGY OF ENAMEL ORGAN 385 



organ, resulting from the establishment of continuity between 

 the capillary lumen and the intercellular spaces of the outer 

 enamel epithelium, following fusion of the endothelium with the 

 latter cells, are in effect foreign bodies in the enamel germ. They 

 are, moreover, treated by the enamel germ as foreign bodies. 

 Groups of cells of the outer enamel epithelium fuse to form 

 giant-cells which ingest these extra vascular erythroplastids. 



Within the enamel pulp occur also spherical and oval globules 

 of varying sizes, especially abundant near the border of the 

 stratum intermedium. These globules were described in a 

 previous paper, and there tentatively interpreted as superfluous 

 enamel secretions on the part of the potential ameloblasts of 

 the stellate reticulum. These globules also are ingested and 

 resorbed by giant-cells, formed in this case by a fusion of cells 

 of the stratum intermedium. 



As regards the stratum intermedium, its formation seems 

 the result also chiefly of the operation of the mechanical factor 

 of pressure. Apparently the mutually opposing pressures 

 of the elongating ameloblasts and the expanding intercellular 

 spaces of the stellate reticulum cause a compression and conse- 

 quent flattening of one or several layers of cells (representing 

 the less differentiated layers of the genxiinative portion of the 

 original oral epithelium) between them, producing thus the so- 

 called stratum intermedium. This interpretation makes intelli- 

 gible the variable presence of the stratum intermedium in typical 

 form throughout the enamel organ. 



h. The enamel orgaii of the white rat 



When we consider, now, the enamel organ of the rat's incisor, 

 as compared with that of the kitten's tooth, we are struck at 

 once with sharp contrasts. In the first place, the enamel organ 

 of the rat's incisor covers only the outer surface of the tooth, 

 including the coronal apex (figs. 4 and 6). A section through 

 the primitive foramen apicis dentis shows a condition essentially 

 hke that of other mammahan teeth (fig. 3). In the second 

 place, this enamel organ is relatively very thin. A typical stellate 

 reticulum is lacking (fig. 5). The inner layer of ameloblasts, 



