TOOTH-DEVELOPMENT IN ORNITHORHYNOHUS. 165 



Fig. 10. — Beta. Section througli tlie postero-iaterual cusp of upper tooth 

 "y," showing the nodule " rfy' " apparently imbedded in the stellate tissue 

 of tiie enamel organ to the labial side of the massive residual dental lamina. 

 X 78. 



Fig. 11. — Beta. High-power view of the toothlet "dy^" showing its central 

 connective-tissue core or pulp enclosed by a distinct ring of dentine, a distinct 

 layer of columnar cells representing the enamel epithelium aud a peripheral 

 capsule of coacentrically arranged connective tissue, x 315. 



Fig. 12. — Beta. Section through the uodule " dx' " to illustrate nodular 

 structure. Note the central cellular core enclosed by concentrically arranged 

 flattened cells forming a compact zone. X 216. 



Fig. 13. — Beta. Section through an epithelial strand to demonstrate its 

 continuity with the enamel epithelium covering the apex of the cusp, x 345. 



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