124 NORMAL HISTOLOGY. 



f Connective tissue matrix. 

 -r, , I Stellate and spindle cells. 



U1 P 1 Odontoblasts. 



[ Blood vessels and nerves. 



Pericementum. The structural elements of this membrane are 

 the fibres, the fibroblasts, the cementoblasts, the osteoblasts, osteo- 

 clasts, and glands. The -fibres are of the white fibrous variety, and 

 their chief function is to hold the tooth in position. The fibroblasts 

 are spindle-shaped cells which occur between the fibres. The osteo- 

 blasts are the bone formers, and are exactly like those of the peri- 

 osteum. The osteodasts are the giant cells which have the power 

 to dissolve calcareous matter. Cementoblasts engage in the forma- 

 tion of the cementum. 



The cementum. This covers the root of the tooth and differs 

 from bone in having no Haversian canals. It is thin at the neck, 

 but becomes thicker toward the extremity of the root. It is made 

 up of lamellae, lacunas, cement corpuscles, and canaliculi. The 

 canaliculi are supposed to communicate with the dentinal tubules. 



Enamel. The enamel exhibits the membrane of Nasmyth, the 

 enamel prisms, and the stripes of Eetzius. The membrane of Nas- 

 mytli is a tough epithelial sheath which covers the crown during its 

 earliest development. The enamel prisms are five or six-sided rods, 

 which extend out perpendicularly from the dentine. When enamel 

 is attacked by acids, it is completely dissolved, which is not true of 

 dentine and cementum. 



Dentine.. Some of the structures of dentine are the dentinal 

 tubules, interglobular spaces, lines of Salter, etc. The dentinal 

 tubules are minute canals, which extend from the pulp to the outer 

 surface of the dentine. Each tubule consists of a sheath called the 

 sheath of Neumann, within which is a dentinal fibril, a prolonga- 

 tion from an odontoblast of the pulp. The lines of Salter are lines 

 which appear in dried specimens, and are probably due to a shrink- 

 age of the tooth. The dentine is composed of twenty-eight per cent 

 of organic matter and seventy- two per cent of inorganic matter. 

 The interglobular spaces consist of uncalcified portions of the ma- 

 trix. They appear as irregular spaces and are sometimes quite abun- 

 dant. 



