DINOSAURIA 269 



sometimes divide once in their course. Each medullary canal 

 is surrounded by a clear space. Its cavity was occupied in 

 the section described by a substance of a deeper yellow colour 

 than the rest of the dentine. 



The dentinal tubes present a diameter of j-^Hoth of an inch, 

 with interspaces equal to about four of their diameters. At the 

 first part of their course, near the pulp-cavity, they are bent in 

 strong undulations, but afterwards proceed in slight and regular 

 primary curves, or in nearly straight lines to the periphery of 

 the tooth. The secondary undulations of each tooth are regular, 

 and very minute. The branches, both primary and secondary, 

 of the dentinal tubes are sent off from the concave side of the 

 main inflections ; the minute secondary branches are remark- 

 able at certain parts of the tooth for their flexuous ramifica- 

 tions, anastomoses, and dilatations into minute calcigerous 

 cells, which take place along nearly parallel lines for a limited 

 extent of the course of the main tubes. The appearance of 

 interruption in the course of the dentinal tubes, occasioned by 

 tins modification of their secondary branches, is represented 

 by the irregularly dotted tracts in the figure. This modifica- 

 tion must contribute, with the medullary canals, though in a 

 minor degree, in producing that inequality of texture and of 

 density in the dentine, which renders the broad and thick tooth 

 of the Ljuanodon more efficient as a triturating instrument. 



The enamel which invests the harder dentine, forming the 

 ridged side of the tooth, presents the same peculiar dirty brown 

 colour, when viewed by transmitted light, as in most other 

 teeth. Very minute and scarcely perceptible undulating fibres, 

 running vertically to the surface of the tooth, form the only 

 discernible structure in it. 



The remains of the pulp in the contracted cavity of the 

 completely formed tooth are converted into a dense but true 

 n^srous substance, characterized by minute elliptical radiated 

 (tils, whose long axis is parallel with the plane of the concen- 



