78 ELEMENTARY PHYSIOLOGY. [VIL 



a. The Dentine. 



a. In the matrix, apparently homogeneous, are 

 numerous dentinal tubules which run in a 

 wavy course from the pulp- cavity outwards. 

 These, dividing as they go, and giving off 

 many anastomosing lateral branches, finally 

 end either in loops or in small irregular 

 cavities, the so-called interglobular spaces, 

 on the surface of the dentine. 



p. In some places the dentinal tubules are cut 

 transversely. Here the central dark spot in- 

 dicates the space formerly occupied by the 

 dentinal fibre, the ring round this is the 

 dentinal sheath. 



1. The Cement or Crusta Petrosa. 



a. This differs little from bone, but Haversian 

 canals are generally absent. 



/?. The canaliculi of the lacunae, next to the in- 

 ter-globular spaces, open into these, thus 

 bringing the dentinal fibres into connection 

 with the bone-corpuscles. 



7. Where the cement is massive, wavy 'contour' 

 lines may be seen, indicating the successive 

 deposits. 



c. The Enamel. 



The striated enamel fibres or prisms are 

 arranged in sets, perpendicular to the sur- 

 face of the dentine. In mounted specimens 

 the indications of the separate fibres are 

 generally not well marked, but are visible at 



