398 H. E. JORDAN 



4. Both the so-called 'papillary layer' and the 'stratum inter- 

 medium' are interpreted as essentially the product of the opera- 

 tion of the mechanical factor of pressure; the former resulting 

 from the impingement of growing capillaries, the latter chiefly 

 from the elongation of the ameloblasts. 



5. There is no histologic evidence that either the papillary 

 layer or the stratum intermedium plays a specific role in amelo- 

 genesis, distinct from that of the extra-ameloblastic portions 

 of the enamel organ as a whole. 



6. Apparent amelopulpar invasions of blood vessels are inter- 

 preted in terms of sections of such vessels pushing obliquely 

 into the periphery of the enamel organ. Such vessels are still 

 separated from the stellate reticulum by a double membrane 

 composed of outer enamel epithelium and endothelium. 



LITERATURE CITED 



Addison, W. H. F., and Appleton, J. L. 1921 On the development of the amelo- 

 blasts of the molars of the albino rat, with special reference to the 

 enamel-free areas. Anat. Rec, vol. 21, p. 43 (Proc. Am. Assoc. Anat.). 



Hopewell-Smith, A. 1918 The normal and pathological histology of the mouth, 

 pp. 263-264. P. Blakiston & Co., Philadelphia. 



Hopewell-Smith, A., AND Tims, H. W. Marett 1911 Tooth germs in the wall- 

 aby, Macropus billiardieri. Proc. Zool. Soc, London. 



Jordan, H. E. 1921 Further evidence concerning the function of the osteo- 

 clasts. Anat. Rec, vol. 20, pp. 281-295. 



Notes, F. B., and Thomas, N. G. 1921 A text-book of dental histology and 

 embryology, p. 332. Lea & Febiger, Philadelphia and New York. 



Rose, C. 1891 Ueber die Entwickelung der Zahne des Menschen. Arch. f. 

 mikr. Anat., Bd. 38, S. 447. 



Skillen, W. G. 1921 A report on the formation of dentin and cementum relative 

 to the structure of the root end. Jour. Nat. Dent. Assoc, vol. 8, pp. 

 1-8. 



Williams, J. Leon 1895 On the formation and structure of dental enamel. 

 Dental Cosmos, vol. 38, pp. 101-127. 



