DENTINE.— ENAMEL.— LENS TISSUE. 



75 



Fig. 67. — Two dentinal cell-., b, 

 which pass with their processes 

 through a portion of the dentinal 

 canals at a. and protrude from 

 the fragment of dentine at c ; af- 

 ter Beale. 



sesses — and at a later stage as well — a similar cell covering. 

 These (Fig. 67 , b), are the dentinal cells or, as they have been 

 characteristically named (Waldeyer), 

 the odontoblasts, the sculptors of the 

 tooth bone. Our cells, oblong, 

 measuring 0.02 to 0.03 mm., are stra- 

 tified. One or more of their fine, 

 thread-like processes penetrate the 

 dentinal tubuli peripherically. An 

 able English investigator, Tomes, first 

 saw such " soft fibres " here. 



The crown is covered with enamel, 

 the hardest substance of the body. The organic form-deter 

 mining basis amounts to only a slight per 

 cent. (3.5 to 6), against a prodigious excess 

 of bone earths. 



The enamel (Fig. 68), a petrified epithe- 

 lial production, consists of long, closely 

 crowded polyhedral cylinders, the enamel 

 prisms or enamel columns {b). They fre- 

 quently appear to pass through the entire 

 thickness of the enamel covering ; their di- 

 ameter is 0.0034 to 0.0045 mm. 



Transverse polished sections of the enamel 

 show a delicate hexagonal mosaic (Fig. 69). 



A peculiar transversely striated appearance may be recog- 

 nized in the isolated enamel prisms. 



The surface of the enamel, finally, is cov- 

 ered by an uncommonly tough membrane. 

 This is the cuticle of the enamel (Fig. 68, a). 



Beneath the enamel the dentinal tubules 

 form loop-like and reticular transitions (Fig. 

 68, d). In the hard brittle substance of 

 the former, there has been a formation of 

 numerous clefts (c), which may communicate with the canals 

 of the dentine. 



With the tolerably simple structure of the teeth, which has 



y. 



Fig. 68. — Peripheral 

 portion of the dentine d, 

 from the crown; with 

 enamel covering,/': a, 

 enamel membrane ; c, the 

 cavities filled with air. 



Fig. 69. — Transverse 

 section of the human 

 enamel prisms. 



