led calvarium, Z B, holds
serial order with the cervical spinous processes, E I, and these with
the dorsal spinous processes. The dura-matral lining membrane, A A A*,
of the cranial chamber is continuous with the lining membrane, C, of the
spinal canal. The brain is continuous with the spinal cord. The
intervertebral foramina of the cervical spine are manifesting serial
order with the cranial foramina. The nerves which pass through the
spinal region of this series of foramina above and below C are
continuous with the nerves which pass through the cranial region. The
anterior boundary, D I, of the cervical spine is continuous with the
anterior boundary, Y F, of the cranial cavity. And this common serial
order of osseous parts--viz., the bodies of vertebrae, serves to
isolate the cranio-spinal compartment from the facial and cervical
passages. Thus the anterior boundary, Y F D I, of the cranio-spinal
canal is also the posterior boundary of the facial and cervical
cavities.

Now as the cranio-spinal chamber is lined by the common dura-matral
membrane, and contains the common mass of nervous structure, thus
inviting us to fix attention upon this structure as a whole, so we find
that the frontal cavity, Z, the nasal cavity, X W, the oral cavity, 4,
5, S, the pharyngeal and oesophageal passages 8 Q, are lined by the
common mucous membrane, and communicate so freely with each other that
they may be in fact considered as forming a common cavity divided only
by partially formed septa, such as the one, U V, which separates to some
extent the nasal fossa from the oral fossa.

As owing to this continuity of structure, visible between the head and
spine, we may infer the liability which the affections of the one region
have to pass into and implicate the other, so likewise by that
continuity apparent between all compartments of the face, fauces,
oesophagus, and larynx, we may estimate how the pathological condition
of the one region will concern the others.

The cranium, owing to its comparatively superficial and undefended
condition, is liable to fracture. When the cranium is fractured, in
consequence of force applied to its anterior or posterior surfaces, A or
B, Plate 20, the fracture will, for the most part, be confined to the
place whereat the force has been applied, provided the point opposite
has not been driven against some resisting body at the same time. Thus
when the point B is struck by a force sufficient to fracture