ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



91 



Fig. 57. Trans-cemental canals in the apex of the root of an upper permanent premolar 

 of a Pacific walrus. Arrows point to three canals; others are evident near them. (Photo by 

 G. C. Kelley) 



Age (years) 



Fig. 58. Thickness of successive layers of cementum on the shaft of the root in post-canine 

 teeth of some Pacific walruses. Each series of interconnected symbols represent data 

 from one male (solid) or female (open). 



