1(32 



MICROSCOPIC .i.v.rroj/r OF THE ORGANS. 



its connection with it. The place of junction which remains is 

 called the neck of the enamel organ (Fig. 119). In the region 

 of the neck the dental ridge grows downward into the connec- 

 tive tissue on the lingual side of the milk tooth, and forms 

 another ridge, in which thickenings occur. Into these the 

 papillae of the permanent teeth grow, so that in the fifth month 

 of foetal life there are present the beginnings of both milk and 

 permanent teeth (Fig. 119). 



Certain changes take place in the enamel organ. The cells 

 bordering on the tooth papilla, the so-called inner enamel cells, 



FIG. 118. 



of 



Dental papilla 



M.J > JL.'%'j3 ^ ^?jf . "_ . v .^ '% % R i* - ^ ** -n^f- dflBi 



An early stage in the development of a tooth in a pig's embryo. X 240. 



become higher, while the outermost layer of cells, the outer 

 enamel cells, become more flat. The cells between these two 

 layers form the enamel pulp (Fig. 119). In the latter region 

 the intercellular substance increases in amount; the cells become 

 stellate and anastomose with one another. As growth goes on, 

 the enamel pulp becomes gradually less in quantity, and finally 

 vanishes almost entirely. Meanwhile the connective tissue 

 around the tooth forms a capsule, the so-called tooth sac. The 

 development of the hard tissues of the tooth begins with the 

 dentine. This is a product of the connective-tissue cells which 

 lie on the surface of the dental papilla, and are known as odon- 

 loblasts. These are columnar cells arranged in a layer. The 

 dentine begins as a thin homogeneous membrane, the membrana 



