928 NEUROLOGY 



and form a plexus with the cervical branch of the facial nerve beneath the Platysma; 

 others pierce that muscle, and are distributed to the skin of the upper and fron~ 

 part of the neck. 



The descending branches (rami inferiores} pierce the Platysma, and are distributee! 

 to the skin of the side and front of the neck, as low as the sternum. 



The Supraclavicular Nerves (nn. supraclavicu lares; descending branches} arise from 

 the third and fourth cervical nerves; they emerge beneath the posterior border 

 of the Sternocleidomastoideus, and descend in the posterior triangle of the neck 

 beneath the Platysma and deep cervical fascia. Near the clavicle they perforate 

 the fascia and Platysma to become cutaneous, and are arranged, according to 

 their position, into three groups anterior, middle and posterior. 



The anterior supraclavicular nerves (nn. supraclamculares anteriores; suprasternal 

 nenes) cross obliquely over the external jugular vein and the clavicular and sternal 

 heads of the Sternocleidomastoideus, and supply the skin as far as the middle line. 

 They furnish one or two filaments to the sternoclavicular joint. 



The middle supraclavicular nerves (nn. supraclamculares medii; supraclavicular 

 nerves} cross the clavicle, and supply the skin over the Pectoralis major and Del- 

 toideus, communicating with the cutaneous branches of the upper intercostal nerves. 



The posterior supraclavicular nerves (nn. supraclamculares posteriores; supra-acromial 

 nerves} pass obliquely across the outer surface of the Trapezius and the acromion, 

 and supply the skin of the upper and posterior parts of the shoulder. 



Deep Branches of the Cervical Plexus. INTERNAL SERIES. The Communicating 

 Branches consist of several filaments, which pass from the loop between the first 

 and second cervical nerves to the vagus, hypoglossal, and sympathetic. The branch 

 to the hypoglossal ultimately leaves that nerve as a series of branches, viz., the 

 descending ramus, the nerve to the Thyreohyoideus and the nerve, to the Genio- 

 hyoideus (see page 916). A communicating branch also passes from the fourth 

 to the fifth cervical, while each of the first four cervical nerves receives a gray 

 ramus communicans from the superior cervical ganglion of the sympathetic. 



Muscular Branches supply the Longus capitis, Rectus capitis anterior, and Rectus 

 capitis lateralis. 



The Communicantes Cervicales (communicantes hypoglossi) (Fig. 804) consist 

 usually of two filaments, one derived from the second, and the other from the third 

 cervical. These filaments join to form the descendens cervicalis, which passes 

 downward on the lateral side of the internal jugular vein, crosses in front of the 

 vein a little below the middle of the neck, and forms a loop (ansa hypoglossi) with 

 the descending ramus of the hypoglossal in front of the sheath of the carotid 

 vessels (see page 916). Occasionally, the loop is formed within the sheath. 



The Phrenic Nerve (n. phrenicus; internal respiratory nerve of Bell) contains motor 

 and sensory fibers in the proportion of about two to one. It arises chiefly from the 

 fourth cervical nerve, but receives a branch from the third and another from the 

 fifth; the fibers from the fifth occasionally come through the nerve to the Sub- 

 clavius. It descends to the root of the neck, running obliquely across the front 

 of the Scalenus anterior, and beneath the Sternocleidomastoideus, the inferior 

 belly of the Omohyoideus, and the transverse cervical and transverse scapular 

 vessels. It next passes in front of the first part of the subclavian artery, between 

 it and the subclavian vein, and, as it enters the thorax, crosses the internal mam- 

 mary artery near its origin. Within the thorax^ it descends nearly vertically in 

 front of the root of the lung, and then between the pericardium and the medias- 

 tinal pleura, to the diaphragm, where it divides into branches, which pierce 

 that muscle, and are distributed to its under surface. In the thorax it is accom- 

 panied by the pericardiacophrenic branch of the internal mammary artery. 



The two phrenic nerves differ in their length, and also in their relations at the 

 upper part of the thorax. 





