ON THE YOMERINE TEETH OE CTENODUS. 119 



at the junction of the base with the crown ; their course is now 

 directly parallel to the vertical axis of the tooth, and they are 

 almost parallel to each other ; branching still occurs, but not so 

 frequently as in the base, and the branches are given o:fi: at a 

 more acute angle. This arrangement of the canals gives the 

 crown the appearance of being composed of a series of upright 

 tubes (Fig. XYII) when a vertical section is examined under a low 

 power. The canals are smaller in diameter than those in the 

 base and also more uniform in size throughout their course, the 

 average diameter being 3-o^th of an inch. They are open on all 

 the external surfaces, this giving rise to the pitted appearance 

 thereon. The tissue between the canals is homogeneous and not 

 laminated, and they are in about equal proportions. From all 

 the canals arise calcigerous tubules, which are short and run a 

 straight course ; they branch frequently, and the terminal 

 branches anastomose with those from the nearest vascular canals. 

 The intermediate branches inosculate with others given off by the 

 same trunk or with those arising from neighbouring tubules, but 

 which spring from the same canal. They measure at their 

 origin about -g^o-oo^th of an inch in diameter and the minute 

 branches average about 3iroo"oth of an inch, but the extreme 

 terminal branches can only be observed under a power of 600 

 diameters ; they have, therefore, an exceedingly small, almost 

 immeasurable, diameter. Fig. XIX gives an excellent illustration 

 of the method of branching pursued by these tubules." I may 

 observe that this arrangement is totally different from that of 

 any tooth structure that I have investigated under the micro- 

 scope, whether fossil or otherwise. " The tubules arise by a 

 comparatively large trunk, which immediately gives of£ from all 

 sides a number of short fine tubules, some of which are larger 

 and longer than the others. These larger branches in their turn 

 give off minute branches in the same manner as the parent stem ; 

 the trunk of the tubule after proceeding a short distance divides 

 into two main branches, which give off two sets of tubules like 

 the main portion of the tubule. This process of double division 

 goes on until anastomosis takes place with the terminal branches 

 of a tubule from a neighbouring canal. Each tubule and its 

 main branches divide dichotomously. Although the figure I 

 have exhibited shows the peculiar structure very fairly, it requires 

 at least 600 diameters to do so perfectly, and even under that 

 high power it requires a trained eye to detect the minute branches 

 dividing once again. I cannot better express in words the 

 peculiar method of branching of the tubules' and the main 

 branches than by remarking that they are ' feathered.' " 



Such is the account I gave of a vomerine tooth of Ctenodus m 

 my papers to the " Monthly Eeview of Dental Surgery" for 

 May and June, 1874 ; but at that time I considered it to be a 



