56 ANATOMY OF THE HEAD AND NECK 



It follows a course a little different on one side from that 

 on the other ; on the right side the nerve passes in front of 

 the subclavian artery, between it and the vein ; on the left 

 side it passes between the left subclavian and common 

 carotid, and then crosses the arch of the aorta ; below these 

 points the two nerves resemble each other in their course, 

 which is behind the root of the lung, along the oesophagus, 

 to the stomach. As the right pneumogastric crosses the 

 subclavian, it gives off the recurrent laryngeal branch which 

 curves around that vessel, and is reflected upward to the 

 larynx ; on the left side this branch is given off as the nerve 

 crosses the aorta, and it curves around its arch at the point 

 where the ductus arteriosus is obliterated, to ascend like 

 its fellow. In their course upward the recurrent branches 

 lie on the inner side of the carotids, between the oesopha- 

 gus and the trachea, to both of which they give branches ; 

 they terminate by filaments distributed to all the muscles 

 of the larynx except the crico-thyroid, which is supplied by 

 the superior laryngeal nerve. 



The PHRENIC NERVE is a medium-sized nerve arising from 

 the anterior trunks of the third and fourth cervical nerves, 

 and occasionally from the fifth ; it descends obliquely upon 

 the anterior scalenus muscle, crossing from its outer to its 

 inner edge, and enters the thorax between the subclavian 

 artery and vein, passing in front of the root of the lung, 

 upon the pericardium, to the diaphragm, to which it is dis- 

 tributed. 



The ARCH OF THE AORTA gives rise to three vessels, 

 collectively known as the brachio-cephalic trunks ; the in- 

 nominata, the left carotid, and the left subclavian ; the 

 number is sometimes increased by the left vertebral, which 

 in a certain number of instances arises from the aorta, in- 

 stead of from the left subclavian ; when this irregularity 

 takes place the supernumerary vessel is usually given off 

 between the carotid and subclavian arteries. Occasionally, 

 the number of primary branches is reduced to two. A very 

 slight interval separates the aortic trunks from each other. 



The INNOMINATA ARTERY is a short trunk, three quarters 

 of an inch in length; it lies upon the trachea, which it 

 crosses somewhat obliquety, and then divides into the right 

 carotid and right subclavian arteries. The innominata 

 occasionally gives off a branch called the middle thyroid, 

 which ascends tortuously in front of the trachea to the 

 thyroid body ; the existence of this anomalous branch, it 



