rtained by the touch, in
both instances, even in the undissected body. The thyroid point, O, of
Plate 8, indicates the line, R N, which the carotid artery traverses in
the same figure, along the anterior border of the sterno-mastoid muscle,
as seen in the dissected region of Plate 7. The mid-point of the
clavicle, U, Plate 7, and the top of the sternum in the same figure,
will, while the eye follows the arching line, Z X T V, indicate with
correctness the arching course of the subclavian, such as is represented
in the dissection of that vessel, B, Plate 8.

The subclavian artery has no special sheath, properly so called; but the
deep layer of the cervical fascia, P, Plate 8, which passes under A, the
clavicular portion of the sterno-mastoid muscle, and becomes of
considerable thickness and density, sheaths over the vessel in this
region of its course.

A very complex condition of the veins which join the external jugular at
this part of the course of the subclavian artery is now and then to be
found overlying that vessel. If the hemorrhage consequent upon the
opening of these veins, or that of the external jugular, be so profuse
as to impede the operation of ligaturing the subclavian artery, it may
in some measure be arrested by compressing them against the resisting
parts adjacent, when the operator, feeling for D, the scalenus muscle,
and the first rib to which it is attached, cannot fail to alight upon
the main artery itself, B, Plate 8.

The middle of the shaft of the clavicle is a much safer guide to the
vessel than are the muscles which contribute to form this posterior
triangle of the neck, in which the subclavian vessel is located. The
form or position of the clavicle in the depressed condition of the
shoulder, as seen in Plate 8, is invariable; whereas that of the
trapezius and sterno-mastoid muscles is inconstant, these muscles being
found to stand at unequal intervals from each other in several bodies.
The space between the insertions of both these muscles is indefinite,
and may vary in degrees of width from the whole length of the clavicle
to half an inch; or, as in some instances, leaving no interval whatever.
The position of the omo-hyoid muscle will not be accounted a sure guide
to the locality of the subclavian artery, since, in fact, it varies
considerably as to its relationship with that vessel. The tense cords of
the brachial plexus of nerves, F, Plate 8, which will be found, for the
most part, ran