Dental cosmos . ee dental shells in Fig. 6 are invested by a common enamel-organ, with a strongly developed enamel-pulp and external epithe-lium. The end of the dental ridge is only slightly constricted offfrom that enamel-organ. As soon as the three shells fuse with oneanother, the enamel-pulp and outer epithelium commence to degener- 1116 THE DENTAL COSMOS. ate. But the inner enamel epithelium remains functional for sometime, until the formation of enamel has ceased. The enamel epi-thelium in Fig. 7 stops close to the lower end of the right dentalshell. In some sections the fusion of the she
Dental cosmos . ee dental shells in Fig. 6 are invested by a common enamel-organ, with a strongly developed enamel-pulp and external epithe-lium. The end of the dental ridge is only slightly constricted offfrom that enamel-organ. As soon as the three shells fuse with oneanother, the enamel-pulp and outer epithelium commence to degener- 1116 THE DENTAL COSMOS. ate. But the inner enamel epithelium remains functional for sometime, until the formation of enamel has ceased. The enamel epi-thelium in Fig. 7 stops close to the lower end of the right dentalshell. In some sections the fusion of the shells with the maxilla hasalready taken place more anteriorly. The fusion must naturally takeplace as soon as the closely allied tissues, dentine and bone, meet with-out a separating epithelial sheath. I succeeded also in one case in showing macroscopically a stage inthe Charmeleon in which only the two anterior dental shells of the lastmolar were fused, while the posterior one was still isolated (Fig. i). Fig. Fig. 5.—Cha»iarleo?i 1 nlgarisy 22 cm. long. Posterior cusp of the penultimate and firstindication of the last molar from the upper jaw. DK, dentine germ of the penultimate molar ;SP, enamel pulp ; , maxilla ; ZL, dental ridge; Pp, papillae of the last developing molar,ioodiam. The development of the teeth of the Chamaeleon furnishes a strikingproof of the theory that the molars are formed by coalescence, whichI uphold, together with some other workers. The essential character of a single tooth is that it be invested bythe columnar cells of the inner enamel epithelium. This only furnishesthe matrix which determines the form of the tooth. The form of thedental roots is partly determined by the inner enamel epithelium ofthe epithelial sheath. I have shown in various places that the dentalridge, with the enamel-organ developing from it, is nothing but a por-tion of the epithelium of the jaws which has grown down into themesoderm. In most fishes and Amphibia, and al
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