158 A MANUAL OF DENTAL ANATOMY. 



three times as long 1 as the corresponding cells lower down upon the 

 dentine papilla, are in the position of the terminal cap of enamel 

 which characterises these teeth. Moreover in the tooth sac of the 

 poison fang of a viper, the distribution of the large cells coincides 

 with that of the enamel on the finished tooth. 



Calcification of the Dentine. The dentine is formed 

 upon the surface of the dentine bulb, or papilla, from with- 

 out inwards, so that no portion of dentine once calcined can 

 receive any increase in external dimensions ; all additions 

 must take place upon the interior of the dentine cap. The 

 nature of the dentine bulb has already been to some extent 

 described ; it remains to consider somewhat more minutely 

 the nature of its surface. The cells constituting the mem- 

 brana eboris, to which Waldeyer has given the convenient 

 name of " odontoblasts," form an exceedingly sharply denned 

 layer upon the surface of the dentine wall, being arranged 

 in a single row ; the cells immediately beneath them differ 

 strongly from them, so that there is not so marked an 

 appearance of transitional structure as may be seen in the 

 stratum intermedium of the enamel organ. Nothing what- 

 ever like the linear succession of formative cells, which, by 

 coalescence at their ends went to form the dentinal tubes, 

 as described by the older writers, is to be seen. 



The odontoblast cells vary in form according as the den- 

 tine formation is actively going on or not, but at the period 

 of their greatest activity they are broad at the end directed 

 towards the dentine cap, so as to look almost abruptly 

 truncated. The several processes of the cells have already 

 been described; there are, however, sometimes several 

 " dentinal processes " proceeding from a single cell, and 

 Boll has counted no less than six. 



The cells are finely granular, and are, according to 

 Waldeyer and Boll, destitute of all membrane ; the nucleus 

 is oval, lies in that extremity of the cell which is farthest 

 from the dentine, and is sometimes prolonged towards the 

 dentinal process so as to be ovoid or almost pointed. 



