( 4 ) 



the cup for the joint of the lower jaw is very broad and the result 

 of this is again that the pterygoid processes have approached each 

 other closely. Further changes appear at the frontal side of the skull- 

 base by the size of the alveoles of the tusks. 



The alveolar outer wall shows a lateral projection as with the 

 walrus, only slightly more massive ; the distance between the two 

 projections is consecjuently also somewhat greater than with the 

 walrus. We divide this distance again by the breadth of the skull : 

 the fossil lies at the end of the variation series of the walrus. But 

 the size of the tusk-alveoles produces still another difference. It 

 causes namely the rows of teeth to be squeezed together, so that 

 the distance of the two incisors, compared with the breadth of the 

 skull, is extremely small. But this also occurs with some old wal- 

 ruses. Moreover the lower side of the upper jaw differs in shape : 

 in the walrus it is broad and hollowed, in the fossil narrow and flat. 



The lateral face of the skull presents in more than one respect a 

 great difference with the walrus, namely in the shape of the tusks. 

 In all the former properties the fossil approached the old walruses 

 and if also the tusks had little deviated from theirs, the reasons for 

 making a distinction would have been rather feeble. But this is not 

 the case. The curvature of the tusks is with the fossil much stronger 

 than with the walrus. If we determine the radius of curvature 

 of all the tusks, we find it in the fossil to be 27 centimetres, for 

 the walrus never under 38 cms. It must be noted that such a small 

 radius of curvature only occurs with young, female walruses with 

 relatively weak teeth. In older animals, however, with which we 

 must compare our skull, the radius of curvature was never under 

 45 cms. and mostly over 50 cms. Whereas in the former properties 

 the fossil resembles the old walruses, it deviates very strongly from 

 them in regard to the shape of the tusks. Also the tusks are more 

 elegant and the right tooth shows deep longitudinal grooves. 



From the tusks we may also draw a conclusion as to the age of 

 the animal. With young individuals the pulp cavity is very deep ; 

 with advancing age it gradually tills with osteodentine. With the 

 fossil now the pulp cavity only had a depth of 3,5 cm. Also the 

 thickness of the tusks is greater in the middle than at the base, 

 which points to the period of strongest growth for the teeth being- 

 passed. 



Again the considerable corrosion of the teeth point to an elderly 

 individual. 



If we now summarise the results of the comparison of the fossil 

 with the walrus, we may stale: 



