ernal jugular, scapular, and other
veins.

D. Scalenus anticus muscle stretching over the artery, and separating it
from the internal jugular vein.

E. Post-half of omo-hyoid muscle.

F. Inner branches of the brachial plexus of nerves.

G. Clavicular portion of trapezius muscle.

H. Transversalis colli artery.

I. Layer of the cervical fascia, which invests the sterno-mastoid and
trapezius muscles.

K. Lymphatic bodies lying between two layers of the cervical fascia.

L. Descending superficial branches of the cervical plexus of nerves.

M. External jugular vein seen under the fascia which invests the
sterno-mastoid muscle.

N. Platysma muscle cut on the body of sterno-mastoid muscle.

O. Projection of the thyroid cartilage.

P. Layer of the cervical fascia lying beneath the clavicular portion of
the sterno-mastoid muscle.

Q. Layer of the cervical fascia continued from the last over the
subclavian artery and brachial plexus of nerves.

[Illustration: Right side of the head and neck, showing blood vessels,
muscles and other internal organs.]
Plate 8

COMMENTARY ON PLATES 9 & 10.

THE SURGICAL DISSECTION OF THE STERNO-CLAVICULAR OR TRACHEAL
REGION, AND THE RELATIVE POSITION OF ITS MAIN BLOODVESSELS,
NERVES, &c.

The law of symmetry governs the development of all structures which
compose the human body; and all organized beings throughout the animal
kingdom are produced in obedience to this law. The general median line
of the human body is characterized as the point of fusion of the two
sides; and all structures or organs which range this common centre are
either symmetrically azygos, or symmetrically duplex. The azygos organ
presents as a symmetrical unity, and the duplex organ as a symmetrical
duality. The surgical anatomist takes a studious observation of this law
of symmetry; and knowing it to be one of general and almost
unexceptional occurrence, he practises according to its manifestation.

The vascular as well as the osseous skeleton displays the law of
symmetry; but while the osseous system offers no exception to this law,
the vascular system offers one which, in a surgical point of view, is of
considerable importance--namely, that behind the right sterno-clavicular
articulation, C, Plate 9, is found the artery, A, named innominate, this
being the common trunk of the right common carotid and subclavian
vessels; while on the left side, behind the left sterno-clavicular