264 



THE DIGESTIVE SYSTEM 





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dental sac, which incloses the entire dental germ and finally, by 

 gradually encroaching upon the narrow neck which still connects 

 the enamel germ with the dental ridge, severs the connection of 



these organs so that the 

 primitive tooth lies free 

 within the dental sac. The 

 outer enamel epithelium, 

 which lines all portions of 

 the dental sac except at 

 the base of the dental pa- 

 pilla, forms several layers 

 of flattened epithelial cells. 

 Remnants of this cell layer 

 frequently persist, in rela- 

 tion to the inner margin of 

 the bony alveolus whose 

 wall is produced by intra- 

 membranous ossification in 

 the connective tissue sur- 

 rounding the embryonic 

 dental sac. 



/ The Enamel Pulp. This 

 structure is produced by a 

 most remarkable differen- 

 tiation which occurs within 

 the mid-portion of the en- 

 amel organ. The epithe- 

 lial cells of this region, 

 which at first appear to 

 form a delicate syncytium, become separated by wider and wider in- 

 tercellular spaces, and are thus drawn out into stellate forms with 

 long anastomosing processes. The resulting cells closely resemble 

 in form the connective tissue cells of embryonic or gelatinous con- 

 nective tissue. They are, however, inclosed on all sides by the 

 epithelial cells of the inner and outer enamel epithelium and, like 

 other epithelial tissues, are never penetrated by blood vessels. 



The enamel pulp appears to serve a purely mechanical func- 

 tion, it being a soft tissue through which the growing tooth readily 

 pushes its way to the surface. 



THE DENTAL PAPILLA, The dental papilla is a connective 

 tissue structure which is invested by and grows into the enamel 



FIG. 222. A PORTION OF FIG. 221, NEAR THE 



APEX OF THE DEVELOPING TOOTH. 



a, enamel epithelium; 6, adamantoblasts ; c, 

 enamel; d, dentine; e, odontoblasts;/, border 

 of the dental pulp. Hematein and eosin. x 550. 



