208 EVOLUTION AND DISEASE. 
or osteo-dentine, thus encysting the missile. In due 
course this foreign body moves onward with the segment | 
of the tusk in which it is embedded, and eventually 
comes to lie in the exserted portion of the tusk until it 
is liberated by wear or the skill of the ivory-turner. 
The entrance of a bullet is readily understood. The — 
great force by which they are propelled carries them A 
easily through animal structures, but with spear-heads | 
it is rather different. Mr. Charles Tomes?! gives an < 
intelligible explanation of this condition in connection — 
with the head of a spear embedded in an elephant’s tusk 
preserved in the museum of the Odontological Society of 
Great Britain. It is to be presumed that a heavily-loaded 
spear was dropped by a native from a tree, with the © 
intention of its entering the brain, upon the elephant as ! 
it was going to water. But in this case the spear pene- 
trated the open base of the growing tusk, which looks 4 
almost vertically upwards, and then the iron point . 
appears to have broken off. This did not destroy the 
pulp, but the tooth continued to grow, and the iron 
point, twenty centimetres long and four in width, became 
so completely enclosed that there was nothing upon the — 
exterior of the tusk to indicate its presence. 
The museums of the Royal College of Surgeons, 
England, and Odontological Society of Great Britain, 
contain many excellent specimens of foreign bodies 
embedded in the tusks and molar teeth of elephants, as 
well as masses of osteo-dentine removed from tusks 
apparently healthy. |Osteo-dentine, in all respects 
similar to that formed in tusks under diseased con- 
* “ Dental Anatomy,” Ist ed., p. 322. 
