LESSON 53.] THE STRUCTURE OF THE TEETH. 191 



enamel of such a tooth from the dentine at its point of junction. 

 This plan of attachment appears only to be used for teeth like the 

 canines, that are brought violently into contact with resisting sub- 

 stances; other teeth, the molars for example, having a steady, uni- 

 form action to perform, do not require such extraordinary care, nei- 

 ther is it bestowed upon them. To show the mode of connection 

 with the enamel of a molar tooth, see Fig. 307. 



The dentinal tubuli are seen at a, their terminations dividing into 

 two branches (b) prior to reaching the enamel (c), which forms the 

 mode of connection of the two tissues. 



822. The junction of dentine with the crusta petrosa, or cemen- 

 tum, is also by the insertion, or interlacement, of the terminal bifid 

 dentinal tubuli with the cementum ; and as there is no strain or vio- 

 lence to any part of the fang, tins mode of connection appears to be 



Fro. SOT. FIG. 308. 



Connection of Ivory and Enamel, Molar Junction of Ivory and Crusta 



Tooth. Petrosa. 



all that is necessary. It is interesting to observe that whether the 

 dentine has to be connected to the enamel or to the crusta petrosa, 

 that its own tubuli are employed as the bond of union. 



The fang of a tooth, from its position in the bony socket of the 

 jaw (alveolus), is greatly protected from acts of violence ; whilst the 

 same appliances are in use to join the crusta petrosa to the dentine, 

 the branches of the tubes of ivory are so minute as to be scarcely 

 distinguishable. For the most part, the junction of these tissues 

 rather indicates a dark line, of no great depth, in which the divided 

 tubes are scarcely apparent. This will be understood by consulting 

 Fig. 308, which shows the crusta petrosa (a), dentinal tubuli (J), and 

 the junction of the two (c) ; but such is the extreme minuteness and 

 shortness of the divided dentinal tubes in connection with this tissue, 

 that they are scarcely discernible. 



