PHRENIC NERVE 813 
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 brachiocephalicus 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 
mandibular space. 
The third cervical nerve leaves the vertebral canal through the foramen be- 
tween the second and third cervical vertebre. Its dorsal branch emerges between 
two bundles of the intertransversalis muscle, accompanied by a branch of the verte- 
bral artery, turns dorsally 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 longissimus capitis et 
atlantis, rectus capitis ventralis major, longus colli, splenius, and brachiocephalicus. 
It also gives off a large cutaneous nerve which passes out between the two parts of 
the brachiocephalicus 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 brachiocephalicus, 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 cutaneus, 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. 590). 
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 go almost entirely to the brachial plexus; that of the seventh 
nerve contributes the posterior root of the phrenic nerve. 
PHRENIC NERVE 
The phrenic nerve (N. phrenicus) (Figs. 553, 554, 558), the motor nerve to the 
diaphragm, is formed by the union of two or three roots which run obliquely down- 
ward and backward over the superficial face of the scalenus muscle. The chief 
roots come from the ventral branches of the sixth and seventh cervical nerves. The 
root derived from the fifth nerve is small and inconstant. The root from the 
seventh cervical comes by way of the brachial plexus. The nerve crosses the ventral 
border of the scalenus a fingerbreadth in front of the first rib, passes through the 
angle of divergence of the inferior cervical and brachial arteries, and enters the 
thorax by passing between the latter vessel and the anterior vena cava. Beyond 
this the course of the nerve is not the same on both sides. The right nerve courses 
backward and somewhat downward over the right face of the anterior vena cava, 
crosses the pericardium, and continues along the posterior vena cava to the dia- 
phragm. In the latter part of its course it is enclosed in a special fold of the right 
pleura and inclines gradually to the ventral face of the vein. The left nerve, in 
part with the vagus, runs its entire course in the mediastinum. In the anterior 
mediastinum it lies along the lateral face of the brachiocephalic artery ventral to 
