ny various conditions;
and such is the case, in fact. No anatomist can pronounce with exactness
the precise figure of vessels or other organs while they lie concealed
beneath the surface. An approach to truth is all that the best
experience can boast of. The form and relations of the carotid vessels
of Plate 7 may or may not be the same as those concealed beneath the
same region of Plate 8, at the point R.

The motions of the head upon the neck, or of the neck upon the trunk,
will influence the relative position of the vessels A C B, of Plate 7,
and therefore we take a fixed surgical position, in the expectation of
finding that the carotid artery projects from under the anterior border
of the upper third of the sterno-mastoid muscle, opposite the upper
border of the thyroid cartilage; at this situation of the vessels, viz.,
R, Plate 8, opposite O, the thyroid projection, is in general to be
found the anatomical relation of the vessels as they appear dissected in
Plate 7. Of these vessels, the main trunks are less liable to anomalous
character than the minor branches.

The relative position of the subclavian artery is as liable to be
influenced by the motions of the clavicle on the sternum, as that of the
carotid is by the motions of the lower jaw-bone on the skull, or by the
larynx, in its own motions at the fore-part of the neck. It becomes as
necessary, therefore, in the performance of surgical operations upon the
subclavian artery, to fix the clavicle by depressing it, as in Plate 8,
as it is to give fixity to the lower maxilla and larynx, in the position
of Plate 7, when the carotid is the subject of operation.

The same named structures, but different as to their parts, will be
found to overlie the subclavian artery as are found to conceal the
carotid artery. The skin, the fascia, and platysma muscle, the
sterno-cleido-mastoid muscle, the deep layer of the cervical fascia,
&c., cover both vessels. One additional muscle binds down the subclavian
artery, viz., the scalenus anticus. The omo-hyoid relates to both
vessels, the anterior division to the carotid, the posterior to the
subclavian.

The carotid artery lies uncovered by the sterno-mastoid muscle, opposite
to the upper border of the thyroid cartilage, or the hyoid bone; and the
subclavian artery emerges from under cover of a different part of the
same muscle, opposite the middle of the clavicle. These points of
relationship to the skeletal parts can be asce