ior side of this anterior
triangle. Again: taking the points 5 Z Y to mark the posterior triangle
of the cervical square, so will it be seen that the internal jugular
vein and the common carotid artery, with the vagus nerve between them,
range the anterior side of this posterior triangle, while the subclavian
artery, Q, passes through the centre of the inferior side of the
posterior triangle, that is, under the middle of the shaft of the
clavicle.

The main blood vessels (apparently according to original design) will be
found always to occupy the centre of the animal fabric, and to seek
deep-seated protection under cover of the osseous skeleton. The
vertebrae of the neck, like those of the back and loins, support the
principal vessels. Even in the limbs the large bloodvessels range
alongside the protective shafts of the bones. The skeletal points are
therefore the safest guides to the precise localities of the
bloodvessels, and such points are always within the easy recognition of
touch and sight.

Close behind the right sterno-clavicular articulation, but separated
from it by the sternal insertions of the thin ribbon-like muscles named
sterno-hyoid and thyroid, together with the cervical fascia, is situated
the brachio-cephalic or innominate artery, A B, Plates 5 and 6, having
at its outer side the internal jugular division of the brachio-cephalic
vein, W K, Plate 5. Between these vessels lies the vagus nerve, E, Plate
6, N, Plate 5. The common carotid artery, internal jugular vein, and
vagus nerve, hold in respect to each other the same relationship in the
neck, as far upwards as the angle of the jaw. While we view the general
lateral outline of the neck, we find that, in the same measure as the
blood vessels ascend from the thorax to the skull, they recede from the
fore-part of the root of the neck to the angle of the jaw, whereby a
much greater interval occurs between them and the mental symphysis, or
the apex of the thyroid cartilage, than happens between them and the top
of the sternum, as they lie at the root of the neck. This variation as
to the width of the interval between the vessels and fore-part of the
neck, in these two situations, is owing to two causes, 1st, the somewhat
oblique course taken by the vessels from below upwards; 2dly, the
projecting development of the adult lower jaw-bone, and also of the
laryngeal apparatus, which latter organ, as it grows to larger
proportions in the male than in the fe