54 



ELEMENTARY TISSUES. 



Development of Teeth. The teeth, are developed after the 

 following manner : Along the free edge of the tooth- 

 less gum in the foetus, there extends a groove, or small 



Fig. 23.* 



trench, the primitive dental groove (Goodsir), and, from the 

 bottom of this, project ten small processes of mucous mem- 

 brane, or papillce, containing blood-vessels and nerves. As 

 these papillce grow up from below, the edges of the small 

 trench begin to grow in towards each other, and over- 

 shadow them, at the same time that each papilla is cut off 

 from its neighbour by the extension of a partition wall 

 from the gum, which grows in from each side to separate 

 the one from the other. Thus closed in above and all 

 around, each dental papilla is at length contained in a 

 separate sac, and gradually assumes the character of a 

 tooth by deposition on its surface of the various hard 

 matters which have been just enumerated as composing 

 the greater part of a tooth's substance. The small vascular 



* Fig. 23. Enamel fibres ( from Kolliker) 4"- A, fragments and 

 single fibres of the enamel, isolated by the action of hydrochloric acid. 

 B, surface of a small fragment of enamel, showing the hexagonal ends 

 of the fibres. 



