TEETH. 



[ 755 ] 



TEETH. 



tooth, the fine, pale, homogeneous processes 

 of the totith-pulp or deiiliue-fibres. These 

 may be stained by carmine. 



"the ivory not unfrequently exhibits indi- 

 cations of a laminated structure, forming-, 



Eig. 782. 



Portion of tlie ivory, with ivory-globules and inter- 

 globular spaces filled with air. Muguified 350 diams. 



in longitudinal sections, curved lines more 

 or less parallel to the outline of the crown 

 (fig. 731), appi\aring as rings in transverse 

 sections, and called the contour-lines. 



Fig. 733. 



Cement and ivory of the fang of a tooth of an old 

 person, a, cavity; b, ivory; c, cement with lacunse ; 

 e. Haversian canals. Magnified oO diameters. 



Near the enamel (fig. 731) and the cement 

 (fig. 7:29 d) also, the ivory presents one or 

 more irregular dark patches or bands, often 

 continuous -with the ends of the contour- 



lines, and exhibiting a coarsely cellular 

 appearance. On careful examination, the 

 d.irk appearance is seen to result from a 

 number of irregular spaces filled with air 

 (fig. 732 a) iiitevveniiig between certain 

 globules, called ivory-<jlohules, the spaces 

 being termed the interf/hhular sjMces. In 

 the recent tooth, these spaces are filled with 

 the organic basis of the ivory, containing 

 tubes likethe rest of that substance, in which, 

 however, the inorganic matter has not been 

 deposited ; hence this structure arises from 

 imperfect development. 



Other, ill-defined iridescent stripes, run- 

 ning parallel to the pulp-cavity, are some- 

 times seen ; these correspond to the primary 

 curves of the ivory-tubes. 



The cement or bone of teeth forms the 

 outer coating of the fangs (figs. 726 & 733, c), 



Fig. 734. 



Enamel-fibres, isolated by the very slight action of 

 muriatic acid ; human. Magnified 130 diameters. 



sometimes cementing them together. It 

 commences as a very thin layer at the part 

 where the enamel ceases, increasing in 

 thickness towards the ends of the fangs. 

 The cement does not differ from bone in 

 structure, except in rarely containing Ha- 

 versian canals. In the molar teeth of old 

 persons, however, these are met with 

 (fig. 733 e). The lacunae are frequently 

 absent from the "thinner portion of the ce- 

 ment ; and it sometimes contains tubes like 

 those of the ivory. The interlacunar sub- 

 stance is sometimes striated, and exhibits a 

 laminated structure. 



The enamel (fig. 72G a) covers the ivory 



3c2 



