230 GIGANTIC TERRESTRIAL SAURIANS. 
in weight, by being internally hollow, and having 
their cavities filled with the light material of 
marrow, while their cylindrical form tended also 
to combine this lightness with strength.* 
The form of the teeth shows the Megalo- 
* The medullary cavities in the fossil bones of Megalosaurus, 
from Stonesfield, are usually filled with calcareous spar. In the 
Oxford Museum there is a specimen from the Wealden fresh- 
water formation at Langton, near Tunbridge Wells, which is 
perhaps unique amongst organic remains : it presents the curious 
fact of a perfect cast of the interior of a large bone, appa- 
rently the femur of a Megalosaurus, exhibiting the exact form 
and ramifications of the marrow, whilst the bone itself has 
entirely perished. The substance of this cast is fine sand, 
cemented by oxide of iron, and its form distinctly represents 
all the minute reticulations, with which the marrow filled the 
intercolumniations of the caucelli, near the extremity of the 
bone. It exhibits also casts of the perforations along the 
internal parietes, whereby the vessels entered obliquely from 
the exterior of the bone, to communicate with the marrow. 
A mould of the exterior of the same bone has been also formed 
by the sandstone in which it was imbedded : hence, although the 
bone itself has perished, we have precise representations both of 
its external form and internal cavities, and a model of the mar- 
row that filled this femur, nearly as perfect as could be made by 
pouring wax into an empty marrow-bone, and corroding away 
the bone with acid. The sand which formed this cast must have 
entered the medullary cavity by a fracture across the other extre- 
mity of the bone, which was wanting in the specimen. 
From this natural preparation of ancient anatomy we learn 
that the disposition of marrow, and its connection with the reti- 
culated extremities of the interior of the femur, were the same in 
these gigantic Lizards of a former world, as in medullary cavities 
of existing species. 
