SUBCLAVIAN ARTERIES. 



615 



vessels ; others (as Cruveilhier) insist upon 

 the clavicle as the line of demarcation between 

 these two great trunks ; but the stages above 

 assigned to the subclavian arteries are strictly 

 in accordance with the views of British ana- 

 tomical authorities. 



The subclavian vein may be divided into 

 two stages, which correspond to the second 

 and third stages of the artery ; at the inner 

 edge of the scalenus anticus muscle on each 

 side of the neck, the subclavian joins the in- 

 ternal jugular vein to form the vena inno- 

 minata (of Mcckel), which latter vein conse- 

 quent/)/ corresponds to the first stage of the 

 subclavian artery. 



As the right and left subclavian arteries 

 differ from each other essentially in their first 

 stage, it is necessary to describe them sepa- 

 rately in this portion of their course. 



First stage of the right subclavian artery. 



This portion of the vessel varies from one 

 to two inches in length ; it extends from the 

 summit of the arteria innominata to the tra- 

 cheal edge of the anterior scalenus muscle, and 

 passes in a direction outwards, and slightly 

 upwards. At its commencement it lies to the 

 right of the trachea, and is concealed by the 

 sterno-clavicular articulation. 



In this stage the artery is contained in the 

 antero-inferior triangle of the neck. The fol- 

 lowing structures here constitute its anterior 

 relations, and are described in the order in 

 which they present themselves in dissection : 



The skin, and subcutaneous cellular stra- 

 tum, with one sheet of the cervical fascia, 

 being divided, the tendon of the sterno-mas- 

 toid muscle (sternal origin) is exposed : be- 

 hind it is a cellular interval of constant ex- 

 istence, though of variable extent, where 

 anastomosing veins and small arterial twigs 

 ramify. The outer edges of the sterno-hyoid 

 and of the sterno-thyrcid muscles are more 

 deeply placed ; the latter extends much fur- 

 ther outwards than the former, and hence it 

 more directly overhangs and conceals the 

 subclavian artery. These muscles are con- 

 tained in distinct sheaths (furnished by the 

 deep cervical fascia), which isolate them, as 

 well from the superficial as from the deeper- 

 seated parts : the layer of fascia which forms 

 the back of the sheath of the sterno-thyroid 

 muscle is the deepest lamina of the cervical 

 aponeurosis ; towards the middle line it in- 

 vests the front of the trachea, and the deep 

 thyroid veins; externally, it covers the carotid 

 and subclavian arteries, with their accompany- 

 ing veins, and is connected to the scalenus 

 anticus muscle, whilst, interiorly, it is attached 

 to the clavicle, to the sternum, and to the 

 " thoracico-cervical septum," through the in- 

 tervention of which it is connected with the 

 fibrous layer of the pericardium. On the 

 removal of this fascia from the region under 

 consideration, the immediate anterior relations 

 of the subclavian artery are exhibited ; they 

 are as follow : 



a. The right vena innominala, its satellite 

 vein, lies anterior to the artery in the first 

 stage of its course, but on a lower plane, and 



separated from it by the phrenic and vagus 

 nerves, and by the internal mammary artery. 



b. The internal jiign/nr vein, which passes 

 downwards and outwards into the subclavian 

 vein, in order to form with it the right vena 

 innominata, crosses the front of the artery 

 nearly at right angles : an interval (the result 

 of the inclination outwards of the internal 

 jugular vein) occurs between this vein and 

 the common carotid artery ; and here 



c. The vagus nerve passes over the sub- 

 clavian artery ; whilst internal to this point 

 the subclavian artery is enveloped ma. nervous 

 sheath, formed of 



d. The cardiac filaments of the sympathetic 

 nerve.* 



c. Lastly, the phrenic nerve constitutes an 

 important anterior relation of the subclavian 

 artery, passing anterior to the very last por- 

 tion of the first stage of the vessel, though 

 not in contact with it. The trajet of the 

 nerve is external to that of the internal jugular 

 vein, which, as before mentioned, crosses the 

 same aspect of the artery. There is no actual 

 contact between the phrenic nerve and the 

 subclavian artery, because the nerve, as it 

 leaves the inner margin of the scalenus an- 

 ticus muscle, lies on and crosses the origin of 

 the mammary artery, which thus separates 

 the nerve in question from the trunk of the 

 subclavian. The relation of 



f. The vertebral vein, to the subclavian ar- 

 tery, is subject to much variety. According 

 to the descriptions of most anatomists, it 

 passes posterior to the artery ; but the writer 

 has found this vein nearly as often in front of 

 the artery as behind it ; and occasionally he 

 has seen the vertebral vein terminate in two 

 branches, of which one passed on the anterior, 

 and the other on the posterior aspect of the 

 subclavian artery, so as to encircle that vessel 

 before they opened into the vena innominata. 

 When the vertebral vein is single, and passes 

 over the front of the subclavian artery, it 

 usually lies internal and parallel to the in- 

 ternal jugular vein. 



The anterior relations of the first stage of the 

 right subclavian artery, are, therefore, the fol- 

 lowing : 



1. Integument, subcutaneous areolar tissue, 



fascia. 



2. Sterno-mastoid muscle, sterno-clavi- 



cular articulation. 



3. Sterno-hyoid and thyroid muscles, iso- 



lated from one another, and from the 

 last-named muscle, by layers of the 

 cervical fascia. 



4. The deep layer of the cervical aponeurosis. 



5. The phrenic and vagus nerves, and the 



cardiac filaments of the sympathetic 

 nerve. 



6. The right innominate, and internal jugu- 



lar veins, and sometimes 



7. The vertebral vein. 



The remaining relations of the artery in its 

 first stage are the following: 



Inferiorly, it corresponds to the loop of the 



* Vide art. NECK, vol. iii. note to p. 575. 



