male, will cause the interval at
this place to be much greater in the one than the other. In the infant,
the larynx is of such small size, as scarcely to stand out beyond the
level of the vessels, viewed laterally.

The internal jugular vein is for almost its entire length covered by the
sterno-mastoid muscle, and by that layer of the cervical aponeurosis
which lies between the vessels and the muscle. The two vessels, K C,
Plate 5, with the vagus nerve, are enclosed in a common sheath of
cellular membrane, which sends processes between them so as to isolate
the structures in some degree from one another.

The trunk of the common carotid artery is in close proximity to the
vagus nerve, this latter lying at the vessel's posterior side. The
internal jugular vein, which sometimes lies upon and covering the
carotid, will be found in general separated from it for a little space.
Opposite the os hyoides, the internal jugular vein lies closer to the
common carotid than it does farther down towards the root of the neck.
Opposite to the sterno-clavicular articulation, the internal jugular
vein will be seen separated from the common carotid for an interval of
an inch and more in width, and at this interval appears the root of the
subclavian artery, B, Plates 5 and 6, giving off its primary branches,
viz., the thyroid axis, D, the vertebral and internal mammary arteries,
at the first part of its course.

The length of the common carotid artery varies, of course, according to
the place where the innominate artery below divides, and also according
to that place whereat the common carotid itself divides into internal
and external carotids. In general, the length of the common carotid is
considerable, and ranges between the sterno-clavicular articulation and
the level of the os hyoides; throughout the whole of this length, it
seldom or never happens that a large arterial branch is given off from
the vessel, and the operation of ligaturing the common carotid is
therefore much more likely to answer the results required of that
proceeding than can be expected from the ligature of any part of the
subclavian artery which gives off large arterial branches from every
part of its course.

The sympathetic nerve, R, Plate 6, is as close to the carotid artery
behind, as the vagus nerve, N, Plate 5, and is as much endangered in
ligaturing this vessel. The branch of the ninth nerve, E, Plate 5,
(descendens noni,) lies upon the common carotid, i