ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



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Fig. 91. Focal abrasion on the medial surface of the tusks: left, anteromedial view of 

 the mouth of a 25-year-old female, showing foci of medial abrasion adjacent to the lower 

 jaw; right, anterior view of the tusks of an old female in which are two deeph- worn foci 

 of medial abrasion in the distal half and one broader focus proximalh": lower, antero- 

 medial view of the right tusk of an old female, showing deep medial abrasion. (Photos bv 

 F. H. Fay and G. C. Kelley) 



of the anterior surface usually is most intense in adult males. 



In most males and in nearly all females, the posterior aspect of the tip of each 

 tusk is smooth and often highly polished (Fig. 90, right). This burnishing appar- 

 ently is caused by frequent contact with the skin of the breast, for the polish is 

 most intense on those tusks with the greatest parasagittal curvature. 



Loss of tissue by abrasion takes place also on the medial surface of the tusk, 

 where it contacts the lower jaw (Fig. 91). The material removed is mainly 

 cementum, and the primary site of this abrasion is just distal to the gingiva. 



