MO HEAD AND NECK 



capitis lateralis and the scalenus anterior ; the intermediate 

 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 part 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 ; the 

 lower transverse portion of the anterior jugular vein ; and, 

 occasionally, the lower end of the external jugular vein, when 

 that vessel dips forwards 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 lobe of the thyreoid 

 gland also. 



Dissection. Commence by cleaning the anterior rami 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 transverse 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 lower two 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 forwards ; 

 and the dissector must at the same time secure the twigs of con- 

 nection which pass from the medial side of the loop to the hypo- 

 glossal nerve and to the superior cervical ganglion of the sym- 

 pathetic trunk, which lies behind the upper part of the internal 

 carotid artery. 



After the dissector has defined the loops of the plexus he 



