520 Royal Society of Edinburgh. 
and Cuvier on the subject, observed that the principal difficulty has 
been to explain how a tusk—a non-vascular organ—can repair in- 
juries which it has sustained, and e: pecially how shot-holes in its 
parietes are filled up. He remarked that in proceeding to investigate 
this subject two facts should be borne in mind; 1. that a tusk under- 
goes no change from vital action in its tissue or configuration after 
it is once formed; and, 2. that it is an organ of double growth, the 
ivory being formed from without inwards, the cement from within 
outwards. He then proceeded to state, that in all cases of wound of 
the tusk-pulp, the latter ossifies round the wound as the first step to- 
wards the separation of the injured portion from the system. ‘The 
ivory constituting this ossification he termed irregular, and an- 
nounced its anatomical identity with the peculiar ivory which fills 
the cavity of the tusk of the Walrus, and the teeth of the Cetacea, 
consisting of central ramifying Haversian canals, of secondary me- 
dullary tubes, and of terminal wavy bundles of Retzian tubes, inter- 
spersed with irregular cells. The irregular ivory is limited in its 
formation, which is terminated by the closure of the orifices of the 
Haversian canals, and the consequent separation of the enclosed 
portion of ramified pulp, from the general system. After this closure 
of the orifices of the Haversian canals, the irregular ivory assumes 
the appearance of a mass covered with stalactitic processes, and its 
surface stands in the same relation to the surface of the general pulp, 
as to the internal surface of the general ivory of the tusk. Regular 
ivory—that composed of undulating Retzian tubes perpendicular to 
the surface of the pulp—now forms upon the surface of the irregular 
ivory, and the latter at last becomes enclosed. When a musket-ball 
passes across the cavity of a tusk, the wound of the surface of the 
pulp ossifies, but the track does not necessarily do so. There are 
two exceptions, however, the author stated, to the non-ossification 
of the track ; that part of it where the ball lodges, and the whole or 
any part of it which may suppurate or form a sinus. In the first 
case the irregular ivory forms an isolated hollow sphere around the 
ball, and studded with stalactitic masses, such as have heen figured 
by Ruysch, &c., and specimens of which were exhibited to the So- 
ciety ; in the second it assumes the form of a tube or irregular shell 
leading to one of the shot-holes. 
Mr. Goodsir then went over in detail the various kinds of wounds 
which the Elephant’s tusk might sustain, as observed by himself and 
described by others. Foreign bodies may enter the tusk from above, 
- through the base of the pulp, without wounding the ivory. A case of 
this kind is described by Mr. Combe in the Philosophical Transactions, 
A ball may enter through the free portion of the tusk, and the hole 
become closed by the protruding portion of the ossified pulp, and va- 
rious curious appearances may present themselves, according as the 
ball may lodge in the opposite wall, or sink below the level of the shot- 
hole, or be left behind it by the advance of the tusk. Balls or spear- 
heads may also penetrate the tusk through its socket, and these are 
the wounds which have so much puzzled anatomists. In such cases, 
the hole, when filled up, is closed by the ossification of the pulp im- 
