638 THE TEETH. 



narrow, and run either in a rectangular or in an oblique direction to the lamellae, 

 with manifold ramifications. They invariably contain delicate beaded fibers of 

 living matter, which send lateral conical offshoots toward the basis-substance, 

 in a much more irregular distribution than we see in primary dentine. 



Fig. 277, which illustrates the lamellated variety of secondary dentine, 

 exhibits a peculiar feature of dentinal canaliculi in the primary dentine, near 

 its connection with the lamellated formation, viz. : bifurcations of the can- 

 aliculi of the primary dentine, which otherwise do not occur except on their 

 terminations near the enamel and the cementum. 



In this group I would enumerate also those peculiar formations which 

 have long been known by the term of " pulp-stones." The process leading to 

 their production is by no means a mere deposition of lime-salts, but a trans- 

 formation of the pulp-tissue, partly, at least, identical with lamellated dentine. 



The third, and evidently rarest, form of secondary dentine is that known 

 by the term "osteo-dentine." Formations of this kind are either peduncu- 



PD 





SD 



FIG. 277. LAMELLATED VARIETY OF SECONDARY DENTINE. 



PD, primary dentine ; SI>, secondary dentine ; P, margin toward the pulp-cavity, with 

 bay-like excavations, due to pulpitis. The lamellae of the secondary dentine are irregular and 

 pierced by dentinal fibers, which are partly in direct connection with those of the primary 

 dentine. Magnified 500 diameters-. 



lated viz. : in connection with the primary dentine by a stem or they 

 partly fill the pulp-cavity in the shape of a uniform layer. There is a striking 

 resemblance between osteo-dentine and Haversian systems of bone-tissue. 

 The systems greatly vary in size and shape, and are separated from each 

 other by a tissue kindred to primary dentine, but devoid of dentinal canali- 

 culi. Each system has in its center a medullary canal, containing a certain 

 amount of plastids known as medullary elements nay, in some of the sys- 

 tems I have met with a central capillary blood-vessel, which has evidently 

 been in direct union with capillaries of the pulp-tissue. Around the medul- 

 lary canal a system of lamellae is arranged, sometimes pretty regularly, and 

 the lamellae are traversed by delicate radiating canaliculi, closely resembling 



