118 DISSECTION OF THE NECK. 



SECTION X. 



DISSECTION OF THE LEFT SIDE OF THE NECK. 



Directions. In the dissection of the left half of the neck, the differences 

 observable between it and the right side are specially to be studied. 

 AVhen the description of the right side will suffice, reference will be made 

 to it. 



After the neck has been made tense over a narrow block, the anterior 

 part of it is to be prepared as on the opposite side. The description of the 

 right side (p. 67 to 73) is to be used for the anterior triangular space, the 

 sterno-mastoideus, and the depressor muscles of the hyoid bone. 



Next the scaleni muscles and the subclavian vessels are to be learnt. 

 The dissection and description of the muscles on the right side (p. 73 to 

 75), will serve for those on the left, except that the student will meet on 

 the left side with the thoracic duct. 



The thoracic duct is contiguous to the part of the subclavian artery in- 

 side the scalenus muscle. If it is uninjected it looks like a vein, rather 

 smaller than a crow-quill; and it will be found by separating the jugular 

 vein from the carotid artery, about half an inch above the clavicle, cours- 

 ing from beneath the artery to end in the subclavian vein. 



On this side the clavicle may remain articulated, in order that the joint 

 may be learnt. 



The LEFT SUBCLAVIAN ARTERY arises from the arch of the aorta, in- 

 stead of from an innominate trunk, and ascends thence over the first rib 

 in its course to the upper limb. With this difference on the two sides in 

 the origin of the subclavian the one vessel beginning opposite the sterno- 

 clavicular articulation, the other in the thorax it is evident that the 

 length and connections of the part of the artery on the inner side of the 

 scalenus must vary much on opposite sides. 



First part. The part of the artery internal to the anterior scalenus is 

 much longer on the left than the right side, and is almost vertical in direc- 

 tion, instead of being horizontal like its fellow. After leaving the chest 

 it is deeply placed in the neck, near the spine and the oesophagus, and 

 does not rise usually so high above the first rib as the right subclavian. 



Between the artery and the surface are structures like those on the 

 right side, viz., the common teguments with the platysnia and deep fascia, 

 and the sterno-rnastoid, hyoid, and thyroid muscles. Behind the vessel is 

 the longus colli muscle. To the inner side are the oesophagus and the 

 thoracic duct ; and the pleura is in contact with the outer and anterior 

 parts. Its connections lower in the chest are described in the dissection 

 of the thorax. 



Veins. The internal jugular vein is superficial to the artery and paral- 

 lel to it. 



Nerves. The pneumo-gastric nerve lies parallel to the vessel instead 

 of across it as on the right side; and the phrenic nerve crosses over it 

 close to the scalenus. Accompanying the artery are the cardiac branches 

 of the sympathetic, which course; along its inner side to the chest; and 

 beneath it is the inferior cervical ganglion. 



The second and third parts of the artery, viz., beneath and beyond 



