junction, Q, Plate 10, the two vessels (subclavian, B, and carotid, A,)
spring separately from the aortic arch. This fact of asymmetrical
arrangement in the arterial trunks at the fore part of the root of the
neck is not, however, of invariable occurrence; on the contrary,
numerous instances are observed where the arteries in question, on the
right side as well as the left, arise separately from the aorta; and
thus Nature reverts to the original condition of perfect symmetry as
governing the development of even the vascular skeleton. And not
unfrequently, as if to invite us to the inquiry whether a separate
origin of the four vessels (subclavian and carotid) from the aorta, or a
double innominate condition of the vessels, were the original form with
Nature, we find her also presenting this latter arrangement of them. An
innominate or common aortic origin may happen for the carotid and
subclavian arteries of the left side, as well as the right. Hence,
therefore, while experience may arm the judgment with a general rule,
such generality should not render us unmindful of the possible
exception.

When, as in Plate 9, A, the innominate artery rises to a level with C,
the right sterno-clavicular junction, and when at this place it
bifurcates, having on its left side, D, the trachea, and on its right
side, B, the root of the internal jugular vein, together with a, the
vagus nerve, the arterial vessel is said to be of normal character, and
holding a normal position relative to adjacent organs. When, as in Plate
10, A, the common carotid, and B, the subclavian artery, rise separately
from the aortic arch to a level with Q, the left sterno-clavicular
articulation, the vessels having M, the trachea, to their inner side,
and C D, the junction of the internal jugular and subclavian veins, to
their outer side, with b, the left vagus nerve, between them, then the
arterial vessels are accounted as being of normal character, and as
holding a normal relative position. Every exception to this condition of
A, Plate 9, or to that of A B, Plate 10, is said to be abnormal or
peculiar, and merely because the disposition of the vessels, as seen in
Plates 9 and 10, is taken to be general or of more frequent occurrence.

Now, though it is not my present purpose to burden this subject of
regional anatomy with any lengthy inquiry into the comparative meaning
of the facts, why a common innominate trunk should occur on the right of
the median lin