The =cervical nerves= (Nervi cervicales) (Figs. 431, 433, 518, 523)
number eight pairs. Of these the first emerges through the
intervertebral foramen of the atlas, the second through that of the
axis, and the eighth between the last cervical and the first thoracic
vertebræ.
The =dorsal branches= are distributed to the dorso-lateral muscles and
skin of the neck. They divide usually into inner and outer branches. The
internal branches (Rami mediales) run in general across the multifidus
and the lamellar part of the ligamentum nuchæ to the skin of the upper
border of the neck; they supply the deep lateral muscles and the skin.
The external branches (Rami laterales) are chiefly muscular in their
distribution. The dorsal branches of the third to the sixth nerves are
connected by anastomotic branches to form the =dorsal cervical plexus=.
The =ventral branches= are smaller than the dorsal ones—an exception to
the general rule. They increase in size from first to last. They supply
in general the muscles and skin over the lateral and ventral aspect of
the vertebræ, but the last three enter into the formation of the
brachial plexus, and the three preceding the last give off the roots of
the phrenic nerve. An irregular =ventral cervical plexus= is formed by
anastomoses established between the ventral branches. The following
special features may be noted:
The =first cervical nerve= emerges through the intervertebral
(antero-internal) foramen of the atlas. Its =dorsal branch= (N.
occipitalis) passes upward and outward between the obliqui capitis and
the recti capitis dorsales and supplies branches to these muscles, the
scutularis and posterior auricular muscles, and the skin of the poll.
The =ventral branch= descends through the alar (antero-external) foramen
of the atlas, crosses over the ventral straight muscles and the carotid
artery under cover of the parotid gland, and divides into two branches.
The anterior branch enters the omo-hyoideus muscle. The posterior branch
passes downward and backward under cover of that muscle, unites with a
branch of the ventral division of the second cervical nerve, and
continues its course on the ventro-lateral surface of the trachea to
enter the sterno-thyro-hyoideus behind the intermediate tendon. In the
recessus atlantis the ventral branch is connected by one or more twigs
with the superior cervical ganglion of the sympathetic, and a little
lower with the hypoglossal nerve. It also sends branches to the ventral
straight muscles of the head and the thyro-hyoideus. Below the atlas the
ventral branch is crossed superficially by the spinal accessory nerve,
the occipital artery, and the inferior cerebral vein.
The =second cervical nerve= is larger than the first. It emerges from
the vertebral canal through the intervertebral foramen of the anterior
part of the arch of the axis. Its =dorsal branch= ascends between the
complexus and the ligamentum nuchæ and ramifies in the skin of the poll.
The =ventral branch= gives off =muscular branches= to the rectus capitis
anterior major, and =anastomotic branches= to the spinal accessory and
the ventral divisions of the first and third cervical nerves; one of
these crosses over the carotid artery and concurs in the formation of
the nerve to the sterno-thyro-hyoideus mentioned above. The ventral
branch then becomes superficial by passing between the two parts of the
mastoido-humeralis, and divides into posterior auricular and cutaneous
branches. The =posterior auricular nerve= passes upward and forward on
the parotid gland parallel with the posterior border of the
parotido-auricularis to ramify on the convex face of the external ear.
The =cutaneous nerve= of the neck (N. cutaneus colli) crosses the
mastoido-humeralis muscle and turns backward along the course of the
jugular vein. On the lower part of the parotid gland it is connected by
a twig with the cervical cutaneous branch of the facial nerve. It gives
off twigs to the subcutaneous muscles and the skin of the parotid and
laryngeal regions and a long branch which passes forward in the
submaxillary space.
The =third cervical nerve= leaves the vertebral canal through the
foramen between the second and third cervical vertebræ. Its =dorsal
branch= emerges between two bundles of the intertransversalis muscle
accompanied by a branch of the vertebral artery, turns upward on the
multifidus, and divides into several branches which radiate on the deep
face of the complexus. It gives branches to these muscles and to the
skin, and a twig which joins the corresponding branch of the fourth
nerve. The =ventral branch= emerges through the intertransversalis below
the bundle above which the dorsal branch appears. It gives branches to
the trachelo-mastoideus, rectus capitis anterior major, longus colli,
splenius, and mastoido-humeralis. It also gives off a large cutaneous
nerve which passes out between the two parts of the mastoido-humeralis
and divides into several divergent branches.
The =fourth= and =fifth cervical nerves= are distributed in general like
the third. Their =dorsal branches= are united by anastomotic twigs with
each other and with those of the third and sixth nerves to form the
dorsal cervical plexus. The =ventral branch= of the fifth nerve often
contributes a small twig to the phrenic nerve.
The =sixth cervical nerve= has a smaller =dorsal branch= than the fifth.
Its =ventral branch= is larger and goes in part to the brachial plexus;
it supplies twigs to the intertransversales, the longus colli, the
mastoido-humeralis, and the cervical parts of the serratus and
rhomboideus, furnishes a root of the phrenic nerve, and gives off
several considerable subcutaneous branches. One of the latter ramifies
on the thick part of the cervical panniculus, to which it gives
branches; another and larger branch (N. supraclavicularis) sends twigs
to the skin over the shoulder joint, and descends to the skin over the
superficial pectoral muscles (Fig. 466).
The =seventh= and =eighth cervical nerves= have small =dorsal branches=,
which ascend between the longissimus and multifidus, giving twigs to
these muscles, the spinalis and semispinalis, the rhomboideus, and the
skin. Their =ventral branches= are very large and concur in the
formation of the brachial plexus; that of the seventh nerve contributes
the posterior root of the phrenic nerve.