40 



NORTH AMERICAN FAUNA 74 



Fig. 26. Variation in shape and size of os clitorides of Pacific walruses. Upper row (left to 

 right) from animals 16, 16, 3, and 7 years old; lower row from calves less than 1 month 

 old. (Photo by K. L. Austerman) 



1 h to soften the surrounding tissue and allow removal of the fragile bone. Then, 

 I air-dried the bone for several days before weighing it to the nearest milligram. 



A bony os clitoridis was present in 37 (90 % ) of the 41 calves and in 18 (75 % ) of 

 the 24 older animals. In the remaining specimens it seemed to be entirely carti- 

 laginous. The ossified specimens were generally S-shaped, but there was wide 

 variation otherwise in their form and size (Fig. 26). In the calves, the bone was 

 cancellous and fragile, and the shaft tended to be circular in cross section. In the 

 older animals, it was more dense and strong but generally more slender and flat- 

 tened. Overall, there was a trend toward diminution, rather than increase in 

 weight of the bone with increasing age (Fig. 27). 



Uterus 



The length and diameter of the uterine horns were measured in all of the 

 females that I examined. Length was measured along the anterior curvature, 

 from the middle of the bifurcation to the tubal end; diameter was measured 

 midway of the length. Only nonpregnant and nonparturient animals will be 

 considered here; the enlargement of the uterus in pregnancy and its retrogression 

 after parturition will be described in connection with the reproductive cycle. 



The lengths and diameters of the uterine horns in relation to age are shown in 

 Fig. 28. Each point represents the mean for both horns; they rarely differed in 

 size by more than 10 % . The estimated growth curves, fitted visually to both sets 



