636 SPINAL NERVES. 



Miiscular branches supply the Anterior Kecti and Rectus Lateralis muscles: 

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

 it and the second. 



The Communicans Noni (Fig. 343) 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 de- 

 scends 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 n*rve 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 on 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 nerve 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; this filament is found, according to 

 Swan, 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 suprarenal capsule, and inferior vnm 

 cava. From the left nerve, filaments pass to join the phrenic plexus, but with- 

 out any ganglionic 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 occipital 

 triangle, and beneath the Trapezius. 



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

 Scapulaa, 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 those of 

 the first two, pass backwards, and divide, behind the posterior Intertransverse 

 muscles, into external and internal branches. 



The external branches supply the muscles at the side of the neck, viz., the 

 Cervicalis Ascendens, Transversalis Colli, and Trachelo-mastoid. 



The external branch of the second cervical nerve is the largest ; it is often 



