ENAMEL 81 



or spindles in marsupial teeth. In the incisor tooth of 

 one of the Kangaroo -rats many similar spaces filled with 

 granular matter were found half-way across the enamel 

 and a few near the free margin (fig. 38). These spaces 

 communicate with dentinal tubes, and it is significant that 

 in those marsupials in which the tube system is much 

 reduced, bodies exactly like the spindles in human enamel 

 are found at the amelo -dentinal junction and also deeper 

 within its substance, and dentinal tubes are often seen 



FIG. 38. One of the terminal bulbs in the enamel from the 

 same specimen shown in fig. 56. ( x250.) 



passing into these spaces, crossing them and terminating 

 more deeply in the enamel. For this and other reasons dealt 

 with more fully in the section on tubular enamels one would 

 look upon these spindles as due to imperfections in the 

 calcification of the interprismatic substance. The dentinal 

 tubes certainly enter them in many places, but they are 

 not dilatations of these tubes but spaces into which they 

 enter. Von Ebner, writing in 1890, says that the fissure 

 formations in human enamel are the result of a drying up 

 or shrinking of the interprismatic cement substance (66). 

 Pickerill (14) also describes them as 'interprismatic spaces 



