118 OJT THE VOMEEINE TEETH OF CTEXODrS. 



and slightly so from side to side, tHe vertical convexity being 

 most marked wliere the crown rises from the base ; the surface 

 is smooth, shining, and covered with minute pores ; the base 

 is concave vertically and convex from side to side ; it is 

 rough, from the large punctations and the coarse reticulation ; 

 this surface of the base is triangular, and the apex is pointed 

 downwards and curved forwards, giving the base, in a side view, 

 the appearance of a heel (Fig. XY) or process protruded from the 

 back of the tooth proper, as in the teeth of Janassa, but in this 

 case a bony mass unites the anterior and posterior points and 

 makes the whole a solid osseous base. The superior border is 

 convex from side to side, and ends at one extremity very suddenly 

 as though a portion had been broken away, which is not the case, 

 this being a genuine character of the tooth ; there are five 

 denticles on tins margin, those on the most rounded portion being 

 the best defined ; the denticles resemble broad, flattened tuber- 

 cles, \\T.th a smooth and shining surface. 



" In the base the vascular canals are very numerous, and run 

 apparently at right angles to the vertical axis of the tooth ; 

 those near the inferior border are larger than those near the 

 junction of the base with the crown, the decrease in size being 

 gradual, the variation in diameter being from To"oth to -« wth 

 of an inch ; the canals at the inferior border are patent, and at 

 the superior border are continuous with those of the crown ; 

 those that extend to the external surfaces remain open, not being 

 closed in by dentine or ganoine. Brandling occurs freely, the 

 branches being given off apparently at all angles ; a vertical 

 section of the base has, therefore, somewhat of a reticulated 

 appearance (Fig. XYIII). The tissue between the vascular 

 canals is homogeneous, and is not arranged around them in con- 

 centric layers ; the proportion of tissue to the sum of the 

 diameters of the canals is nearly equal, that is, the tissue 

 situated betw^een two canals is on an average about equal to the 

 diameter of one of the canals. From all the medullary canals 

 spring numerous calcigerous tubules, which branch and inosculate 

 very freely ; the branches arising from the same trunk anasto- 

 mosing with each other and mth the branches fi'om neighbour- 

 ing systems ; besides this frequent anastomosis the branches 

 are freely interlaced one with the other, so that it is difficult to 

 examine their arrangement, and it renders the tissue of the inter- 

 spaces dark and cloudy; the course of those that can be examined 

 satisfactorily is observed to be short and wav}^ The average 

 diameter of the tubules at their origins is about e-oVoth of an 

 inch. 



" In the crown the canals are still numerous, and though they 

 are continuous with those in the base, they have undergone 

 certain marked changes in their course, &c., the change occurring 



