108 



NORTH AMERICAN FAUNA 74 



a 



Fig. 72. Diagrammatic views of incremental growth of walrus tusks: (a) annual incre- 

 ments of dentin from youth (bottom) to old age (top), as they would appear if separated 

 from the rest of the tusk; and (b) relation of dentinal and cemental increments as seen in 

 longitudinal section. 



individual layers and the total accumulation of cementum tend to be about two- 

 thirds to three-fourths as great as those in males of comparable age. 



Relation of Hypercementosis to Tusk Development 



All of the walrus' teeth other than the tusks show hypercementosis. This is true 



