52 



NORTH AMERICAN FAUNA 74 



Fig. 34. Longitudinal sections of skin on the palmar surface (left) of the foreflipper 

 of a calf and on the incisive surface (right) of the mandible of an adult. (Photos by S. M. 

 Coulthard) 



or ice, as it is in other mammals (Spearman 1964). The presence of similar 

 epidermis on the incisive surfaces of the mouth implies adaptation to 

 requirements for similar protection and adhesive friction. Since teeth generally 

 are absent or vestigial in this part of the mouth, I assume that the rough, 

 cornified tissue serves mainly in grasping and holding prey, during the feeding 

 process. That is, w^hereas the incisiform teeth perform that function in other 

 pinnipeds, the walrus has nearly lost those teeth in the process of evolution 

 (Repenning and Tedford 1977). In their place, the w^alrus has developed tough, 

 cornified pads which presumably are advantageous for its unique method of 

 feeding. The importance of this development is discussed further in Food and 

 Feeding Behavior. 



I found the cornified layer unusually thick (up to 1.3 mm) also along the 

 dorsal edge of the snout and about the nostrils, whereas it was extremely thin 

 (about 0.125 mm) along the anterior edge of the upper lip (Fig. 35). In the 

 former location, this was parakeratosis but apparently nonpathological, for it 

 was present in all specimens. From the frayed surface of the stratum corneum on 

 the upper edge of the snout, I judge that this area frequently is in contact with 

 abrasive materials, probably while the animal is probing the benthic sediments 

 for food. That is, the heavy cornification there seems to be a normal adaptation 

 that gives added protection to the upper edge of the mystacial pad. 



The thinness of the cornified layer on the edge of the upper lip suggests that 

 this is a very sensitive area, important in tactual sensing and selection of food 

 items. On the upper edge of the oral opening, near the corners of the mouth, are 

 two hairless areas, slightly raised and lacking a cornified layer. Nerve bundles 



