THE ANTERIOR PART OF THE NECK 255 



the subclavian vein note: (i) that the arch which it forms 

 is not so pronounced as the arch of the corresponding 

 artery; (2) that throughout its whole course it lies at a 

 lower level, and upon a plane anterior to the artery; and 

 (3) that it is separated from the artery by the scalenus 

 anterior and the phrenic nerve. In the whole of its course 

 the vein lies posterior to the clavicle. 



The sheath of the subclavian vein is attached to the posterior surface of 

 the costo-coracoid membrane. This is a relation of some practical import- 

 ance ; for, on account of it, a forward movement of the clavicle drags upon 

 the vein, and in cases where the vessel is wounded there is always a danger 

 of air being sucked into the vein by such a movement. 



The tributary of the subclavian vein is the external jugular 

 vein, which joins it at the lateral margin of the scalenus 

 anterior. 



Ductus Thoracicus et Ductus Lymphaticus Dexter. The 

 thoracic duct is the vessel by means of which the chyle and 

 the lymph, derived from by far the greater part of the body, 

 are poured into the venous system on the left side (p. 106). 

 Its terminal or cervical portion is displayed in the dissection of 

 the neck. It is a small, thin-walled vessel, frequently mistaken 

 for a vein, which enters the root of the neck at the left 

 margin of the oesophagus. It is there that it should be 

 sought. At the level of the seventh cervical vertebra it 

 arches laterally and anteriorly, and then downwards, above 

 the apex of the pleura, and it enters the innominate vein in the 

 angle of the union of the internal jugular vein with the 

 subclavian. As the thoracic duct courses laterally it lies at 

 a higher level than the subclavian artery, and passes posterior to 

 the common carotid artery, the vagus nerve and the internal 

 jugular vein, and anterior to the vertebral artery and vein 

 and the thyreo-cervical artery or its inferior thyreoid branch ; 

 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 crosses the 

 first part of the subclavian artery. 



A valve composed of two segments guards its entrance 

 into the innominate vein. 



Ductus Lymphaticus Dexter. The right lymph duct is 

 the corresponding vessel on the right side, but it is a com- 

 paratively insignificant channel which conveys lymph from a 



