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 vertebrae. 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 



