DENDRODUS. 



173 



origin, in others at different distances from their termination, and 

 the branches diverge shghtly as they proceed. Each of the above 

 medullary rays is continued from a short process of the central struc- 

 ture, which is connected by a concave line with the adjoining process, 

 so that the whole periphery of the transverse section of the central 

 coarse reticulo-medullary body of the tooth presents a crenate outline. 

 From each ray and its primary dichotomous divisions, short branches 

 are sent off at brief intervals, generally at right angles with the trunk, 

 or slightly inclined towards the periphery of the tooth. These sub- 

 divide into a few short ramifications like the branches of a shrub, 

 and terminate in irregular and somewhat angular dilatations, simu- 

 lating leaves, but which resolve themselves into radiating fasciculi of 

 calcigerous tubes. There are from fifteen to twenty- five or thirty-six 

 of these short and small lateral branches on each side of the medullary 

 rays. 



In a section of the same tooth, one third from its obtuse summit 

 (PI. 62 B, fig. 3), the irregular central pulp-cavity was lost, and in its 

 place there were a few large medullary canals connected by a fine net- 

 work of smaller canals. This tissue occupied rather more than one third 

 of the diameter of the section. From its periphery there was continued 

 the same system of nearly straight, sparingly dichotomizing, medullary 

 canals, radiating at regular distances from the central tissue to the 

 periphery of the tooth. The radiating canals here also give off" short 

 lateral branches, but these do not terminate in such well marked 

 dilatations as those observable at the base of the tooth : the trans- 

 verse branches here generally spring from short alternate lateral 

 bendings of the main stem. There are about forty radiating medul- 

 lary canals in this part of the tooth, and about fifty in the section 

 taken from the base of the tooth. 



In both sections the angular dilated terminations of the small 

 lateral branches of the medullary rays form, as has been said, the 

 centres of radiation of as many systems of the most minute calci- 

 gerous tubes, each system constituting a lobe of the dentine, separated 

 from the adjoining lobes by an extremely thin layer of cement. In 

 the section nearer the apex of the tooth, the radiating systems of 

 calcigerous tubes, forming similar lobes of dentine are given off 



