FEOM THE EED CEAG OP SUFFOLK. 



219 



outline shown in the figures. A combination of such base-lines as 2 and 3 with such 

 successive attrition-outlines as B, C, D, gives the possible variations of a tusk traceable 

 to the causes of " growth " and " attrition." The base-line 1, with the unworn point- 

 outline A, gives the form of very young tusks. 



Diagram to illustrate the growth and attrition of the Tusk of Walrus: — 

 Fig. 1 with less, and fig. 1' with greater primitive curvature. Oscl, osteodentine ; 

 (hit, dentine ; A, original point of tusk; B, C, D, successive positions of 

 the point, resulting from attrition; 1. Early position of the base of tusk 

 and pulp-cavity ; 2, 3, 4. Successive positions of the base-line and pulp- 

 cavity due to new growth. 



It will be observed that the successive attrition-outlines cut into the osteodentinal 

 core of the tusk ; and this fact enables us, by a careful inspection of the surface of a 

 Walrus-tusk, to determine approximately the amount of wear to which it has been sub- 

 jected. A short tusk is not necessarily an old tusk ; but if it have not its osteodentine 

 largely exposed on the convex border, its form is due to such a combination of 

 growth and attrition as we should obtain in the woodcut by taking the base-line 2, 

 together with the attrition-outline B. 



When we add to the varied combination of various conditions of growth and attrition 

 the primary individual variations of the tusk, viz. greater or less curvature, greater or 



