NERVES OF THE NECK. 613 



municates with the inferior cervical ganglion, and fre- 

 quently with the vagus and its recurrent branch ; at this 

 point it enters the chest between the subclavian artery and 

 vein, and proceeds downward on the side of the pericardium 

 in the middle mediastinum, to the diaphragm, to which it 

 is distributed, sending branches on the right side to the 

 liver and vena cava, and on the left to the oesophagus and 

 stomach. The left phrenic is longer than the right from 

 the direction of the heart to the left side. It has been com- 

 monly considered to be a purely motor nerve, but Laschka's 

 recent researches show that it contains sensory filaments 

 also. He states that it effects a double interchange between 

 the spinal and the sympathetic nerves. It commonly arises 

 only from the fourth cervical nerve. The diaphragmatic 

 branches go to the tendinous centre, the inferior cava, the 

 right auricle, and the liver. 



The posterior cervical plexus is formed by the junction of 

 the posterior branches of the first, second and third cervical 

 nerves. It is situated beneath the complexus. Its branches 

 are called musculo-cutaneous and occipitalis major. 



The musculo cutaneous supplies the complexus and semi- 

 spinalis colli, and then passes through the trapezius to 

 become cutaneous, being distributed to the integuments on 

 the back of the neck and head. 



The occipitalis major comes from the second cervical nerve, 

 takes the course of the occipital artery, and supplies the 

 muscles on the back part of the neck and head. The pos- 

 terior branches of the lower cervical nerves supply the mus- 

 cles and integuments on the lower and back part of the 

 neck and head. 



The bracliial plexus (Fig. 153) is situated at the lower 

 part of the neck in the posterior, inferior, lateral triangle, 

 above the clavicle, and between the mastoid and posterior 

 belly of the digastric muscles. It is formed by the union 

 of the four inferior cervical and first dorsal nerves: the fifth 

 and sixth unite into one trunk ; the eighth cervical and 

 first dorsal also unite into one trunk ; the seventh cervical 

 stands alone for some distance, so that this plexus presents 

 33 



