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PHEENIC NEEVE. 699 



ngus capitis, and the rectus capitis anterior. 2. From the second, third, and 

 urth nerves small branches supply the inter- transverse, longus colli, and longus 

 pitis muscles. 3. From the fourth nerve a branch arises for the upper part of the 

 enus anterior. 



(&) Genio-hyoid and Infra-hyoid Muscles. The descending cervical nerve is formed 

 in front of the internal jugular vein by the union of two slender trunks from the 

 cond and third cervical nerves (communicantes hypoglossi). It forms a loop 

 ' communication in front of the carotid sheath with the descending branch of the 

 ypoglossal nerve (derived ultimately from the first two cervical nerves). This 

 >p of communication is called the ansa hypoglossi. It is often plexiform ; and 

 rom it branches are given to the sterno-hyoid and sterno-thyreoid muscles, and 

 both bellies of the omo-hyoid muscle. The nerve to the sterno-hyoid muscle is 

 often continued behind the sternum, to join, in the thorax, with the phrenic nerve 

 >r the cardiac plexus. 



The thyreo-hyoid and genio-hyoid muscles are supplied by branches of the hypo- 

 lossal nerve, which are also traceable back to the communication between the 

 ypoglossal and the first two cervical nerves. 



The anterior muscles in immediate relation to the median plane of the neck, 

 tween the chin and the sternum, are thus continuously supplied by the first 

 three cervical nerves. The hypoglossal is the nerve of the muscles of the tongue, 

 d it is not certain that it contributes any fibres to the above-named muscles, 

 (c) Diaphragm. The phrenic nerve supplies the diaphragm. 



jSTERvus PHRENICUS. 



The phrenic nerve is derived mainly from the fourth cervical nerve, reinforced 

 y roots from the third (either directly or through the nerve to the sterno-hyoid) 

 and fifth (either directly or through the nerve to the subclavius muscle). It runs 

 downwards in the neck upon the scalenus anterior muscle ; at the root of the neck 

 passes between the subclavian artery and vein, enters the thorax and traverses 

 mediastinum to reach the diaphragm, lying in the middle mediastinum 

 tween the pericardium and pleura, and anterior to the root of the lung. In its 

 urse it presents certain differences on the two sides. In the neck, on the left 

 .de, it crosses the first part of the subclavian artery ; on the right side it crosses 

 e second part. In the superior mediastinum, on the left side, it lies between 

 left subclavian and carotid arteries, and crosses the vagus nerve and the 

 >rtic arch. On the right side it accompanies the innominate vein and superior 

 vena cava, and is entirely separate from the vagus nerve. The left nerve is longer 

 than the right, owing to the position of the heart and the left half of the 

 diaphragm. The right nerve sends fibres along the inferior vena cava through 

 the foramen vense cavse. Eeaching the diaphragm the nerve separates into 

 umerous branches for the supply of the muscle ; some enter its thoracic surface 

 ub-pleural branches), but most of the fibres supply it after piercing the muscle 

 ub-peritoneal branches). 



The branches of the phrenic nerve are 1. Muscular (to the diaphragm); 2. 

 pleural ; 3. pericardiac ; 4. inferior vena-caval ; 5. suprarenal ; and 6. hepatic. 



The branches to the pleura and pericardium arise as the phrenic nerve 

 traverses the mediastinum. The branches to the inferior vena cava, suprarenal 

 gland, and liver arise after communication of the phrenic nerve with the 

 diaphragmatic plexus of the sympathetic on the abdominal surface of the 

 diaphragm. 



Communications of the Phrenic Nerve. 1. The phrenic nerve may communicate 

 ith the nerve to the subclavius muscle. 2. It may communicate with the ansa 

 ylossi, or a branch from it (the nerve to the sterno-hyoid). 3. It frequently com- 

 unicates with the cervical part of the sympathetic. 4. It communicates with the 

 eliac plexus by a junction upon the abdominal surface of the diaphragm with the 

 diaphragmatic plexus on the inferior phrenic artery, in which a small diaphragmatic 

 ganglion is found on the right side. From this junction branches are given off to the 

 inferior vena cava, suprarenal gland, and hepatic plexus. 



