ive position of the object of search. On this account it is
that the surgical anatomist chooses to give a fixed position to the
subject about to be operated on, in order to reduce the number of these
difficulties as much as possible.

In Plate 7 will be seen the surgical relationship of parts lying in the
vicinity of the common carotid artery, at the point of its bifurcation
into external and internal carotids. At this locality, the vessel will
be found, in general, subjacent to the following mentioned structures,
numbered from the superficies to its own level--viz., the common
integument and subcutaneous adipose membrane, which will vary in
thickness in several individuals; next, the platysma myoides muscle, F
L, which is identified with the superficial fascia, investing the outer
surface of the sterno-mastoid muscle; next, the deeper layer of the same
fascia, R S., which passes beneath the sterno-mastoid muscle, but over
the sheath of the vessels; and next, the sheath of the vessels, Q, which
invests them and isolates them from adjacent structures. Though the
vessel lies deeper than the level of the sterno-mastoid muscle at this
locality, yet it is not covered by the muscle in the same manner, as it
is lower down in the neck. At this place, therefore, though the actual
depth of the artery from surface will be the same, whether it be covered
or uncovered by the sterno-mastoid muscle, still we know that the
locality of the vessel relative to the parts actually superimposed will
vary accordingly. This observation will apply to the situation and
relative position of all the other vessels as well. Other occurrences
will vary the relations of the artery in regard to superjacent
structures, though the actual depth of the vessel from surface may be
the same. If the internal jugular vein covers the carotid artery, as it
sometimes does, or if a plexus of veins, gathering from the fore-part of
the neck or face, overlie the vessel, or if a chain of lymphatic bodies
be arranged upon it, as is frequently the case, the knowledge of such
occurrences will guard the judgment against being led into error by the
conventionalities of the descriptive method of anatomists. The normal
relative anatomy of the bloodvessels is taken by anatomists to be the
more frequent disposition of their main trunks and branches, considered
per se, and in connexion with neighbouring parts. But it will be seen by
this avowal that those vessels are liable to ma