the bone,
while the point A is not opposed to any resisting body, then B alone
will yield to the force applied; and fracture thus occurring at the
point B, will have happened at the place where the applied force is met
by the force, or weight, or inertia of the head itself. But when B is
struck by any ponderous body, while A is at the same moment forced
against a resisting body, then A is also liable to suffer fracture. If
fracture in one place be attended with counter-fracture in another
place, as at the opposite points A and B, then the fracture occurs from
the force impelling, while the counter-fracture happens by the force
resisting.

Now in the various motions which the cranium A A B performs upon the top
of the cervical spine C, motions backwards, forwards, and to either
side, it will follow that, taking C as a fixed point, almost all parts
of the cranial periphery will be brought vertical to C in succession,
and therefore whichever point happens at the moment to stand opposite to
C, and has impelling force applied to it, then C becomes the point of
resistance, and thus counter-fractures at the cranial base occur in the
neighbourhood of C. When force is applied to the cranial vertex, whilst
the body is in the erect posture, the top of the cervical spine, E D C,
becomes the point of resistance. Or if the body fall from a height upon
its cranial vertex, then the propelling force will take effect at the
junction of the spine with the cranial base, whilst the resisting force
will be the ground upon which the vertex strikes. In either case the
cranial base, as well as the vertex, will be liable to fracture.

The anatomical form of the cranium is such as to obviate a frequent
liability to fracture. Its rounded shape diffuses, as is the case with
all rotund forms, the force which happens to strike upon it. The mode in
which the cranium is set upon the cervical spine serves also to diffuse
the pressure at the points where the two opposing forces meet--viz., at
the first cervical vertebra E and the cranial basilar process F. This
fact might be proved upon mechanical principle.

The tegumentary envelope of the head, as well as the dura-matral lining,
serves to damp cranial vibration consequent upon concussion; while the
sutural isolation of the several component bones of the cranium also
prevents, in some degree, the extension of fractures and the vibrations
of concussion. The contents of the head, like the contents of al