COMMUNICANS NONI PHRENIC. 565 



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 in front of the atlas to the 

 pneumogastric, hypoglossal, and sympathetic. 



Muscular branches supply the Anterior recti and Eectus lateralis muscles; 

 they proceed from the first cervical nerve, and from the loop formed between it 

 and the second. 



The Communicans Noni (fig. 279) consists usually of two filaments, one being 

 derived from the second, and the other from the third cervical. These filaments 

 pass vertically downwards on the outer side of the internal jugular vein, cross in 

 front of the vein a little below the middle of the neck, and form a loop with the 

 descendens noni in front of the sheath of the carotid vessels. Occasionally, the 

 junction of these nerves takes place within the sheath. 



The Phrenic Nerve (internal respiratory of Bell} arises from the third and 

 fourth cervical nerves, and receives a communicating branch from the fifth. It 

 descends to the root of the neck, lying obliquely across the front of the Scalenus 

 anticus, passes over the first part of the subclavian artery, between it and the 

 subclavian vein, and, as it enters the chest, crosses the internal mammary artery 

 near its root. Within the chest, 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, which 

 separately pierce that muscle, and are distributed to its under surface. 



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

 upper part of the thorax. 



The right 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 vena innominata and 

 superior vena cava. 



The left nerve is rather longer than the right, from the inclination of the heart 

 to the left side, and from the Diaphragm being lower in this than on the opposite 

 side. At the upper part of the thorax, it crosses in front of the arch of the aorta 

 to the root of the lung. 



Each ner ve supplies filaments to the pericardium and pleura, and near the chest 

 is joined by a filament from the sympathetic, by another derived from the fifth 

 and sixth cervical nerves, and, occasionally, by one from the union of the 

 descendens noni with the spinal nerves, which, Swan states, occurs only on the 

 left side. 



From the right nerve, one or two filaments pass to join in a small ganglion 

 with phrenic branches of the solar plexus; and branches from this ganglion are 

 distributed to the hepatic plexus, the supra-renal capsule, and inferior vena cava. 

 From the left nerve, filaments pass to join the phrenic plexus, but without any 

 gangl ionic enlargement. 



DEEP BRANCHES OF THE CERVICAL PLEXUS. EXTERNAL SERIES. 



Communicating branches. The cervical plexus communicates with the spinal 

 accessory nerve, in the substance of the Sterno-mastoid muscle, in the subocci- 

 pital triangle, and beneath the Trapezius. 



Muscular branches are distributed to the Sterno-mastoid, Levator anguli 

 scapulae, Scalenus medius and Trapezius. 



The branch for the Sterno-mastoid is derived from the second cervical; the 

 Levator anguli scapulas receiving branches from the third ; and the Trapezius 

 branches from the third and fourth. 



POSTERIOR BRANCHES OF THE CERVICAL NERVES. 



The posterior branches of the cervical nerves, with the exception of the first 

 two, pass backwards, and divide, behind the posterior Inter-transverse muscles, into 

 external and internal branches. 



