50 



NORTH AMERICAN FAUNA 74 



Table 7. 



Thickness of the hi 



ubher on the sternum, midway between the 





foreliiubs. 















Blubber 



thickness (mm) 



Age class 









and sex 



Month 



No. 



Range 



Mean 



Calves 











r 



May 



3 



19-25 



22 



Adults 











M 



January 



1 



76 



— 



M 



May 



2 



50-52 



51 



M 



June 



3 



44-55 



48 



M 



August 



1 



50 



— 



F 



Februan'b 



2 



51-64 



58 



F 



Marchb 



2 



36-38 



37 



F 



Aprilb 



1 



33 





F 



Max-b 



4 



50-76 



66 



F 



MaN'^ 



7 



30-102 



68 



F 



Junet* 



1 



38 





i^Data from J. J. Burns, F. H. Fay. and K. W. Kenyon (unpublished data). 

 t-Females not carr\ing a full-term fetus or attending a newborn calf. 

 •^Females at full term or having a newborn calf. 



irregularities conform to the smaller dermal papillae. Both types of papillae are 

 highly vascularized, particularly at their apices. 



The primary epidermal waves in my samples had an amplitude of 0.6 to 

 1.5 mm and a period of 0.9 to 1.8 mm; the secondary irregularities were from 

 0.03 to 0.4 mm deep. The outer one-third to one-half of the epidermis comprised 

 35 to 70 layers of cornified cells that were loosely arranged in animals beginning 

 their molt and very compact in all others. Nuclei were obsen ed only in the inner 

 third of these layers in animals beginning their molt but were apparent nearh" to 

 the outer surface in all others. 



The greatest departure from that pattern of cornification was seen on the 

 palmar and plantar surfaces of the fore and hind flippers. In each of those areas, 

 the epidermis was from 1 to 3 mm thick, with a cornified layer making up one- 

 half to three-fourths of the total (Fig. 34). The amplitude of the primary waves 

 was from 1.7 to 4.2 mm, with a period of 1.5 to 3 mm, and the cornified layer 

 was densely compacted, with nuclei apparent at all levels. The outermost surface 

 on the crests of the epidermal waves was frayed from abrasion. 



Areas of rough, highly cornified skin comparable to those on the palmar and 

 plantar surfaces of the flippers were found also in the front of the mouth, over 

 the premaxillary and mandibular symphyses. There, the epidermis was up to 

 2.5 mm thick, and the cornified layer made up two-fifths to one-half of the total 

 (Fig. 34). The primary waves were 0.6 to 1.8 mm high with a period of 1.1 to 

 2.2 mm. The granular layer here was more apparent than in the palms and soles 

 but was only about half as thick. As in the palms and soles, the outermost 

 surfaces of the crests of the waves were greatly frayed from abrasion. 



The rugose, highly cornified epidermis on the palmar and plantar surfaces of 

 the walrus' flippers clearly is advantageous for quadrupedal locomotion on land 



