142 THE HEAD AND NECK 



The Thoracic Duct is closely applied to the left side of the 

 oesophagus, as it leaves the thorax. It ascends into the neck 

 for an inch or sometimes an inch and a half above the clavicle, 

 and then turns laterally behind the carotid sheath and its 

 contents, but in front of the vertebral and the inferior thyreoid 

 arteries. It usually crosses in front of the vertebral vein, but 

 in many cases it passes behind that vessel. On reaching the 

 medial border of the scalenus anterior, the thoracic duct passes 

 downwards to enter the postero-lateral aspect of the union of 

 the subclavian and internal jugular veins of the left side. Some- 

 times it extends farther laterally on to the surface of the scalenus 

 anterior, and it usually crosses the phrenic nerve. As it lies 

 behind the carotid sheath the duct crosses the deep triangle 

 (Fig. 44), where it lies above the level of the first part of the sub- 

 clavian artery. Near its termination the thoracic duct lies in 

 front of the big vessel. It may terminate as a single trunk, 

 or it may break up into a number of small branches, which join 

 the internal jugular and subclavian veins independently of one 

 another. If the duct is injured, its ends must be ligatured if it 

 is impossible to reunite them. 



The thoracic duct drains the lymph from both lower limbs, 

 the abdominal walls and most of the abdominal viscera, and 

 the left half of the thorax. In addition it is joined near its 

 termination by the subclavian trunk, from the left upper 

 limb, and the jugular trunk, from the left side of the head 

 and neck. These two trunks, however, may end independently 

 in the subclavian and internal jugular veins respectively. 



The Subclavian Artery arises, on the right side, from the 

 innominate artery behind the sterno-clavicular joint, and it 

 arches upwards and laterally, disappearing behind the scalenus 

 anterior. On the left side, it arises within the thorax from the 

 arch of the aorta, and it lies behind the left common carotid 

 artery as it enters the neck. The first part of the artery rests on 

 the cervical pleura, and extends as far as the medial border 

 of the scalenus anterior. It forms the oblique lower border of 

 the deep triangle of the neck, and is covered in front by the 

 internal jugular vein and the vagus nerve. On the right side 

 the recurrent nerve arises from the vagus as it crosses the vessel, 

 and it runs upwards and medially deep to the subclavian and 

 common carotid arteries. A detailed description of the relations 

 of this part of the subclavian artery is unnecessary, as it is 

 rarely ligated by the surgeon. 



