THE SUPERIOR CAVAL SYSTEM. 



885 



the fascia which encloses that muscle ; near its termination it is united to the 

 middle layer of the deep cervical fascia, behind which it lies. As a result of these 

 connections the vein does not collapse when empty, and, furthermore, its lumen is 

 enlarged by movements, such as those of inspiration or the raising of the arm, 

 which affect the fascia. 



With the exception of the external jugular and occasionally the anterior 

 jugular, the subclavian vein receives, as a rule, no tributaries, the veins which 

 correspond to the branches of the subclavian artery opening either into the 

 innominate or the external jugular. Occasionally, however, it receives the supra- 

 scapular and the superior intercostal vein (page 896), and the acromial thoracic 

 vein may open into it near its beginning. 



Fig. 761, 



Trapezius 



Descending 

 branches of 

 cervical plexus 



Transverse 

 cervical vessels 



Omo-hyoid 



muscle 



Brachial plexu 

 Suprascapular 



vessels" 



Subclavian artery 



Subclavian vein 



Clavicular portion of 

 sterno-mastoid, cut and 

 turned forward 



External jugular vein 



Anterior scalene muscle 

 Phrenic nerve 



Internal jugular vein 



Sternal portion of 



sterno-mastoid 

 Common carotid artery 



T-Sterno-hyoid muscle 

 ■First rib 



Clavicle 



' Dissection of neck, showing relations of subclavian vein ; clavicle has been 



disarticulated from sternum and dravi'n down. 



Variations. — Occasionally the course of the subclavian vein has the form of a curve which 

 rises above the level of the clavicle and may even bring the vein to lie above the artery. It may 

 pass with the artery behind the scalenus anticus, the artery and vein may exchange places with 

 reference to that muscle, or the vein may divide to form a ring encircling the muscle. Rarely it 

 passes between the subclavius muscle and the clavicle. 



Practical Considerations. — The subclavian vein occupies the acute inner 

 angle between the clavicle and the first rib, and therefore — and on account of its 

 slight resistance — in periosteal or osseous growths from those bones is especially 

 likely to suffer compression. The interposed subclavius muscle usually protects it, 

 as it does the artery and the brachial plexus, from injury in case of fracture (page 259), 

 The vein barely rises above the clavicle, and therefore usually escapes in stab- 

 wounds involving the supraclavicular fossa, while the artery which arches an inch 

 to an inch and a half above that line suffers much oftener. 



The connection of the anterior wall of the vein with the fascia of the subclavius 

 muscle, causing an increase in its calibre during forced inspiration or an elevation of 

 the arm {vide supra), should be remembered in case of wound of this vessel during 



