14,8 Sir Everard Home on the milk tusks , 
the milk tusk ; but then it afterwards has an increase back- 
wards in the space between the tables of the skull, which the 
tusks of the narwhal have not ; and in this growth back- 
wards, which is very slow, corresponding to that of the skull, 
absorption of the upper table previously formed, is produced, 
to make room for it. In this way the sockets of the ele- 
phant’s tusks, which are shallow when the animal is young, 
acquire an increase of depth as the elephant grows up, to give 
it sufficient firmness in the skull to support them in the ex- 
ertions that are made with them. 
A similar absorption to what takes place in the upper table 
of the skull in the elephant, is shown to occur in the dugong ; 
it is however probably at a different period of the animal’s 
growth, as the milk tusk in the elephant is shed between the 
first and second year, and the absorption of the upper table 
many years after ; but in the dugong, the absorption of the 
skull takes place just as the milk tusks begin to extend 
themselves beyond the gums, but the age at which the animal 
has at this time arrived is not known. 
The use of the shallow cup, which appears to be an ap- 
pendage peculiar to the milk tusk of the dugong, forming no 
part of the tusk itself, would appear to be for the purpose of 
receiving the point of the permanent tusk as soon as it is 
formed ; so that as the milk tusk advances in the act of its 
being shed, the other may be directed forwards in the same 
course, which is different from that in which it set out. 
The facts that were brought forward in a former paper upon 
the milk tusks of the narwhal, explained many circumstances 
in the natural history of that animal which were involved in 
obscurity ; and the observations that are now made upon the 
