THE ANTERIOR PART OF THE NECK 159 



and as it runs downwards to its termination it is separated 

 from the scalenus anterior by the transverse cervical and 

 transverse scapular arteries and the phrenic nerve. Further, 

 as it approaches the point at which it ends, it lies anterior 

 to the first part of the subclavian artery (Figs. 55, 56). 



A valve composed of two semilunar segments guards its 

 entrance into the innominate vein. 



The right lymph duct is the corresponding vessel on the 

 right side, but it is a comparatively insignificant channel 

 which conveys lymph from a much more restricted area. It 

 commences in the root of the neck, where it is formed by 

 the union of the broncho-mediastinal^ trunk with the sub- 

 clavian and jugular lymphatic trunks of the right side. It 

 terminates in the commencement of the innominate vein 

 by opening into it in the angle of union of the subclavian 

 and internal jugular veins. As in the case of the thoracic 

 duct, its orifice is guarded by a double valve. Through 

 the broncho-mediastinal trunk it receives lymph from the 

 intercostal glands which lie in the upper intercostal spaces 

 of the right side, and from the thoracic visceral lymph 

 glands of the right side ; and, through the right subclavian 

 and jugular lymph trunks, lymph is poured into it from the 

 right upper extremity and the right side of the head and 

 neck, respectively. It constitutes, therefore, the main lymph 

 drain for the following districts: (i) right upper limb ; (2) 

 right side of the head and neck; (3) upper part of right 

 thoracic wall ; (4) right side of diaphragm and upper surface 

 of liver; (5) thoracic viscera on right side of median plane, 

 viz., right side of the heart and pericardium and the right 

 lung and pleura. But not uncommonly the broncho-medi- 

 astinal, the right jugular and subclavian lymph trunks open 

 separately into the internal jugular, the subclavian or the inno- 

 minate vein. 



Cervical Pleura. The pleural sac of each side, with the 

 apex of the corresponding lung, projects upwards into the 

 root of the neck, and the dissector should now examine the 

 height to which it rises, and the connections which it estab- 

 lishes. Its height, with reference to the first pair of costal 

 arches, varies in different subjects. In some cases it extends 

 upwards for two inches above the sternal end of the first 

 rib ; in others, for not more than one inch. The differences 

 depend on the degree of obliquity of the thoracic inlet. 



