tic arch ranges, not alone transversely, but also from
before backward, and to the left side of the dorsal spine; and
consequently, as the innominate artery, A, Plate 9, springs from the
first or fore part of the aorta, while the left carotid and subclavian
arteries arise from the second and deeper part of its arch, the vessels
of both sides rising into the neck perpendicularly from the root in the
thorax, will still, in the cervical region, manifest a considerable
difference as to antero-posterior depth. The depth of the left
subclavian artery, B, Plate 10, from cervical surface, is even greater
than that of the left common carotid, A, Plate 10, and this latter, at
its root in the aortic arch, is deeper than the innominate artery. Both
common carotids, A A, Plates 9 and 10, hold nearly the same
antero-posterior depth on either side of the trachea, M, Plate 10, and
D, Plate 9. Although the relative depth of the arterial vessels on both
sides of the trachea is different, still they are covered by an equal
number of identical structures, taking the same order of superposition.

On either side of the episternal cervical pit, which, even in the
undissected body of male or female, infant or adult, is always a
well-marked surgical feature, may be readily recognised the converging
sternal attachments of the sterno-mastoid muscles, L G, Plate 10; and
midway between these symmetrical muscular prominences in the neck, but
holding a deeper level than them, is situated that part of the trachea
which is generally the subject of the operation of tracheotomy. The
relative anatomy of the trachea, M, Plate 10, D, Plate 9, at this
situation requires therefore to be carefully considered. The trachea is
said to incline rather to the right side of the median line; but perhaps
this observation would be more true to nature if it were accompanied by
the remark, that this seeming inclination to the right side is owing to
the fact, that the innominate artery, A, Plate 9, lies obliquely over
its fore part, near the sternum. However this may be, it certainly will
be the safer step in the operation to regard the median position of the
trachea as fixed, than to encroach upon the locality of the carotid
vessels; and to make the incision longitudinally and exactly through the
median line, while the neck is extended backwards, and the chin made to
correspond with the line of incision. And when the operator takes into
consideration the situation of the v