THE ANTERIOR PART OF THE NECK 239 



tendon of the omo-hyoid, and the lower and posterior part of 

 the sterno-hyoid and sterno-thyreoid. 



Arteries. The upper part of the common carotid (the 

 lower part is still concealed by the lower parts of the omo- 

 hyoid and the lower parts of the sterno-hyoid and sterno- 

 thyreoid muscles) ; the transverse scapular and its sterno- 

 mastoid branch ; the transverse cervical ; the sterno-mastoid 

 branch of the superior thyreoid ; the occipital and its sterno- 

 mastoid branches. 



Veins. The greater part of the internal jugular vein ; a 

 part of the lower transverse portion of the anterior jugular 

 vein ; and, occasionally, the lower end of the external jugular 

 vein when that vessel dips anteriorly to its termination. 



Nerves. The cervical plexus and its branches, including 

 the phrenic nerve ; part of the accessory nerve. 



If the lower parts of the divided sterno-hyoid and sterno- 

 thyreoid muscles are displaced downwards, the lower part of 

 the common carotid and the commencement of the first part of 

 the subclavian artery will be exposed. Crossing the front of 

 the latter are the lower portion of the cervical part of the vagus 

 and a strand of sympathetic fibres called the ansa subclavia ; 

 on the left side, the subclavian artery and the ansa are con- 

 cealed by the commencement of the innominate vein. At 

 the same time the middle thyreoid vein will be exposed, 

 and the posterior border of the lateral lobe of the thyreoid 

 gland also. 



Dissection. Commence by cleaning the anterior branches of the cervical 

 nerves from the second to the eighth, as they emerge between the muscles 

 attached to the tubercles of the transverse processes of the cervical 

 vertebrae. The first nerve, which turns downwards anterior to the trans- 

 verse process of the atlas, will be exposed later. As the upper nerves are 

 cleaned the dissectors will find that the second is connected to the third, 

 and the third to the fourth, by looped strands, convex posteriorly, which 

 constitute the two lower loops of the cervical plexus. The second nerve is 

 connected with the first also by a loop, convex anteriorly, which passes 

 upwards anterior to the transverse process of the atlas and posterior to the 

 upper part of the internal jugular vein. It can be exposed if the vein is pulled 

 anteriorly ; and the dissector must at the same time secure the twigs of 

 connection which pass from the medial side of the loop to the hypoglossal 

 nerve and to the superior cervical ganglion of the sympathetic trunk, which 

 lies behind the upper part of the internal carotid artery. 



After he has defined the loops of the plexus he should trace the remains 

 of the small occipital, the great auricular, the transverse cutaneous nerve of 

 the neck and the supraclavicular branches, which he displayed in the 

 posterior triangle, to their origins from the roots of the plexus. The 

 communicating branches which pass anteriorly to the descendens hypoglossi 

 from the second, and sometimes also from the third cervical nerve, must be 



