essel A, Plate 9, and A, Plate 10,
at this region of the neck, he will at once own to the necessity of
opening the trachea, D, Plate 9, M, Plate 10, at a situation nearer the
larynx than the point marked in the figures. The course taken by the
common carotid arteries is, in respect to the trachea, divergent from
below upwards; and as these vessels will consequently be found to stand
wider apart at the level of K, I, Plate 10, than they do at the level of
M, Plate 10, so the farther upwards from the sternum we choose the point
at which to open the trachea, the less likely are we to endanger the
great arterial vessels.

In addition to the fact, that the carotid arteries at an inch above the
sternum lie nearer the median line than they do higher up in the neck,
it should always be remembered, that the trachea itself is situated much
deeper at the point M, Plate 10, D, Plate 9, than it is opposite the
points F and K of the same figures. The laryngo-tracheal line is, in the
lateral view of the neck, downwards and backwards, and therefore it will
be found always at a considerable depth from cervical surface, as it
passes behind the first bone of the sternum, midway between both
sterno-mastoid muscles.

In the operation of tracheotomy, the cutting instrument divides the
following named structures as they lie beneath the common integument: If
the incision be made directly upon the median line, the muscles F,
sterno-hyoid, and E, sterno-thyroid, Plate 9, are not necessarily
divided, as these structures and their fellows hold a somewhat lateral
position opposite to each other. Beneath these muscles and above them,
thus encasing them, the cervical fascia, f f, Plate 10, is required to
be divided, in order to expose the trachea. Beneath f f the cervical
fascia, will next be felt the rounded bilobed mass of the thyroid body,
lying on the forepart of the trachea; above the thyroid body, the
cricoid and some tracheal cartilaginous rings will be felt; and since
the thyroid body varies much as to bulk in several individuals of the
same and different sexes, as also from a consideration that its
substance is traversed by large arterial and venous vessels, it will be
therefore preferable to open the trachea above it, than through it or
below it.

On the forepart of the tracheal median line, either superficial to, or
deeper than, the cervical fascia, the tracheotomist occasionally meets
with a chain of lymphatic glands or a plexus of vei