THE NECK. 71 



As the subclavian artery leaves the scalene triangle, or while it is still within this space, it 

 gives off 



5. The posterior scapular artery, which passes between the trunks of the brachial plexus and 

 runs parallel to the transversalis colli (by which vessel it is occasionally replaced) beneath the 

 insertion of the levator anguli scapula;, where it subdivides into an ascending and a descending 

 branch.* 



In ligating the subclavian artery as it passes over the first rib, the posterior scapular, the 

 suprascapular, and the transversalis colli arteries must be carefully avoided. Special attention 

 must also be paid to the external jugular vein, which should be divided between two ligatures to 

 avoid the entrance of air emboli. The deeper we penetrate in this region, the more it behooves 

 us to remember that the pleural sac projects above the superior aperture of the thorax (see 

 page 101). 



The internal jugular vein is external to the common carotid artery and, as in the carotid 

 triangle, partly overlies this structure; behind the sternoclavicular articulation it unites with the 

 subclavian vein to form the innominate vein. The lower more or less dilated portion of the in- 

 ternal jugular vein is known as the inferior bulb of the vein. The subclavian vein lies in front of 

 and somewhat below the artery of the same name (in Fig. 27 the outer portion of the vein has been 

 displaced slightly upward), the two vessels being separated by the insertion of the anterior scalene 

 muscle. This vein receives the external jugular, the anterior jugular (frequently a tributary of 

 the external jugular), the acromiothoracic, the suprascapular, and the posterior scapular veins. 



The cervical plexus, formed by the anterior divisions of the four upper cervical nerves, lies 

 upon the origins of the muscles forming the floor of the lateral cervical region and is covered by the 

 sternocleidomastoid muscle. 



The small anterior division of the first cervical nerve communicates particularly with the 

 superior cervical ganglion and forms a loop with the second cervical nerve, from which the muscles 

 of the neck receive their branches. Muscular branches are also given off by the second cervical 

 nerve (to the levator anguli scapulae, for example). This nerve, and frequently the third cervical 

 as well, gives off the fine filaments which pass anteriorly and unite with the descendens hypoglossi 

 to form the ansa hypoglossi. The occipitalis minor (see page 68) usually arises from the loop 

 connecting the second with the third cervical nerve. The auricularis magnus (see page 68) and 

 the superficial colli (see page 68) are given off from the third or from the loop connecting the 

 third with the fourth cervical nerve; the supradavicular nerves are given off from the fourth or 

 from the third and fourth cervical nerves, while the phrenic (see page 104) usually originates 

 exclusively from the fourth cervical. There is a communicating branch connecting the fourth 

 cervical nerve with the brachial plexus, the large roots of which may be seen in the upper 

 portion of the scalene triangle above the subclavian artery. The phrenic nerve runs downward 

 upon the anterior scalene muscle and enters the thoracic cavity by passing between the sub- 

 clavian artery and vein (see Plate 8). 



*The author's nomenclature and description of the branches of the subclavian artery differ considerably 

 most English versions. This is not of great importance, however, when one considers the wide vanatw 

 the structures themselves. ED. 



