THE CERVICAL PLEXVX 



1027 



filaments usually join to form the descendens cervicis, which passes downward 

 on the outer side of the internal jugular vein, crosses in front of the vein a litt!*' 

 .below the middle of the neck, and forms a loop (ansa hypoylossi) with the descend- 

 ens hvpoglossi in front of the sheath of the carotid vessels. Occasionally, the 

 junction of these nerves takes place within the sheath. 



ANTERIOR 



DIVISION OF 



FOURTH CERVICAL* 



SUPRASCAPULA 



| 



DESCENDING 

 BRANCH OF 

 HYPOGLOSCAL 



ANSA 

 HYPOGLOSSI 



THYROID 



AXIS 



INTERNAL 



MAMMARY 



ARTERY 



SUBCLAVIAN 



BRANCH TO 

 PHRENIC 



ANTERIOR 

 THORACIC 



FII;. 757. The right brachial plexus with its short branches, viewed from in front. The Sternomastoid 

 and Trupezius muscles have been completely, the Omohyoid and Subclavius have been partially, removed; 

 a piece has been sawed out of the clavicle; the Pectoralis muscles have been incised and reflected. (Spalteholz.) 



The Phrenic or the Internal Respiratory Nerve of Bell (n. phrenicus) (Figs. 755 and 

 7ol>) arises chiefly from the fourth cervical nerve, with a few filaments from the 

 third and a branch from the fifth, although this branch is occasionally derived 

 from the nerve to the Subclavius. It descends to the root of the neck, running 

 obliquely across the front of the Scalenus anticus, and beneath the Sternomastoid, 

 the posterior belly of the Omohyoid muscles, and the transversalis colli and 

 suprascapular vessels. It next passes over the first part of the subclavian artery, 

 between it and the subclavian vein, and, as it enters the thorax, crosses the internal 

 mammary artery near its origin. Within the thorax it descends nearly vertically 

 in front of the root of the lung and by the side of the pericardium, between it and 

 the mediastinal portion of the pleura, to the Diaphragm, where it divides into 

 branches, some few of which are distributed to its thoracic surface, but most of 

 which separately pierce that muscle and are distributed to its under surface (rami 

 phren-icoaMominal,es}. In the thorax it is accompanied by a branch of the internal 

 mammary artery, the arteria comes nervi phrenici. The two phrenic nerves differ 

 in their length, and also in their relations at the upper part of the thorax. 



The right phrenic nerve is situated more deeply, and is shorter and more vertical 

 in direction than the left; it lies on the outer side of the right innominate vein 

 and superior vena cava. 



