98 A MANUAL OF DENTAL ANATOMY. 



tissue investment, which have to some extent preserved their 

 individuality during calcification. 



In the fresh condition it appears probable that the lacunae 

 are filled up by soft matrix, which shrinks up, and so leaves. 

 them as cavities in dried sections. It can hardly as yet be 

 said that the question of the contents of lacunae has been 

 finally settled, though the researches of Bodecker and Heitz- 

 mann have gone far towards doing so. 



According to them each lacuna contains a protoplasmic- 

 body, which they term the cement corpuscle, with a central 

 nucleus. 



This nucleus may be large and surrounded by but little- 

 protoplasm, or it may be small ; or there may be many 

 nuclei. 



The cement corpuscles communicate freely with one another 

 by offshoots, those of large size occupying the conspicuously 

 visible canaliculi of the lacunae, whilst the finer offshoots are 

 believed by them to form a delicate network through the 

 whole basis substance or matrix. The cement corpuscles near 

 to the external surface give off numerous offshoots which 

 communicate with protoplasmic bodies in the periosteum. 

 By this means the cementum can remain alive even when 

 the pulp of the tooth is dead, and thus the tooth is in no- 

 way a mere foreign body, dead and inert. 



Like bone, cementum is also sometimes found to contain 

 Sharpey's fibres ; that is to say, rods running through it at 

 right angles to its own lamination, and, as it were, perforat- 

 ing it. These are probably calcified bundles of connective 

 tissue. 



Where the cementum is very thin, as, for instance, where 

 it commences at the neck of a human tooth, it is to all 

 appearance structureless, and does not contain any lacuna), 

 and therefore no protoplasmic bodies : nevertheless lacuna* 

 may be sometimes found in thin cementum, as, for example, 



