LÖNNBERG, THE DENTITION OF DELPHINAPTERUS LEUCAS. 5 



In the other teeth the cusps are worn away, but even 

 in such cases when the tooth is so much worn that it is 

 evenly conical, and the remnant of the crown is flush with 

 the root, the limit between the two components is visible 

 indieating the different microscopical structure of the mate- 

 rial. To this question about the structural differences in 

 different parts of the teeth we shall return again låter on. 



In still older skulls than the one just referred to with a 

 basicranial length of 47 V2 cm. it can hardly be expected to be 

 found any remains of the crown of the teeth. But it is really 

 still visible as a wart on the hindmost tooth of the upper 

 jaw in a skull with a basicranial length of nearly 49 cm. 

 Most of the teeth of that skull are, however, obliquely worn 

 off by grinding against each other. The same is the case 

 with all the teeth except the hindmost in a skull with a 

 basicranial length of about 60 cm. 



The dentition of the latter skull is remarkable by the 

 great difference in size of the different teeth, especially tliose 

 of the upper jaw. This difference can to a certain extent be 

 expressed by the measurements of the transversal diameter 

 of each tooth at its base where it protrudes from the jaw. 

 This measurement is, counting from the first and backwards, 

 resp. 13, 16, 14, 13, 13, 11, 9, 9 and 6 mm. In the lower 

 jaw the teeth in the middle of the series are the largest with 

 a basal transversal diameter of about 13 mm. and the same 

 measurement of the hindmost is about 8 mm. This consid- 

 erable difference in size between the different teeth of an old 

 White whale proves in what high degree each individual tooth 

 is able to increase in size independently of the growth of its 

 neighbours, for in the beginning all the teeth are subequal 

 in size. As the growth of the teeth is continuous it does not 

 appear unlikely that the different members of the dentition 

 are stimulated during their development in a different degree 

 as their function and the pressure, to which they are subjected, 

 are not the same in every situation. Those which were most 

 exposed to the pressure should then be impelled to a stronger 

 growth than those which were only little used. For such an 

 interpretation speaks the fact that the hindmost teeth that 

 certainly are subjected to the least wearing, are the smallest 

 of all, and in some skulls of old White whales quite thin and 

 rudimentary teeth are found behind the others. 



