816 



SUBCLAVIAN ARTERIES. 



recurrent nerve, which sometimes has an an- 

 terior relation to the artery also, in consequence 

 of its arising from the pneumogastric at an 

 unusual height in the neck. 



Superiorly , it gives off the vertebral artery 

 opposite a triangular interval, between the 

 scalenus anticus and longus colli muscles. 



Posteriorly, it corresponds from within out- 

 wards, to the transverse process of the seventh 

 cervical vertebra, to the inferior cardiac fila- 

 ments and inferior cervical ganglion, of the 

 sympathetic nerve, to the recurrent nerve, and 

 finally, to the cone of the pleura. 



Nearly the cuter half of the posterior sur- 

 face of this portion of the subclavian artery 

 is thus closely related to this serous sac, being 

 usually that part of the vessel which is ex- 

 ternal to the origin of the vertebral branch, 

 and covered on its anterior surface by the 

 internal jugular vein. 



First stage of the left subclavian artery. 

 The subclavian artery on the left side arises 

 within the thorax, from the termination of 

 the second stage of the arch of the aorta, at 

 the level of the second dorsal vertebra ; it 

 thence assumes a direction nearly vertically 

 upwards, to the inner margin of the scalenus 

 anticus muscle, and lies to the left side of, and 

 anterior to, the two upper dorsal vertebrae, 

 from which it is but a short way distant. 



Whilst in the cavity of the thorax, the left 

 subclavian artery corresponds, posteriorly, to 

 the inferior cervical ganglion, and cord of the 

 sympathetic nerve, to the thoracic duct, and 

 more remotely to the longus colli muscle and 

 spinal column. Anteriorly, it is in relation with 

 the pleura, and more immediately with the left 

 pneumogastric and phrenic nerves (the latter 

 descends parallel to the artery, but the former 

 crosses it very obliquely, from above down- 

 wards and inwards), with the vertebral vein, 

 the confluence of the internal jugular and 

 left subclavian veins, and the great venous 

 trunk which they form by their confluence, 

 viz. the left vena innorninata. Internal and 

 posterior to the artery are placed the oesopha- 

 gus and the left recurrent nerve ; internal 

 and anterior to it, is the left common carotid 

 artery ; whilst external to the artery, through- 

 out the entire of its thoracic stage, are the 

 left lung and pleura. 



After a course within the thorax of about 

 two inches and a half, the left subclavian 

 artery pierces the "thoracico-cervical septum," 

 inclines outwards and a little forwards, and 

 attains the tracheal edge of the scalenus anti- 

 cus muscle, when it bends abruptly outwards ; 

 this terminating portion of the first stage of 

 the vessel (which alone belongs to the cervi- 

 cal region) has, anterior to it, the left internal 

 jugular vein, the vagus and phrenic nerves, 

 and the thoracic duct, just before its termina- 

 tion in the great subclavian vein ; in addition 

 to these relations, the left subclavian has the 

 same coverings as the corresponding portion 

 of the subclavian artery on the right side. 



Differences between the right and the left 

 subclavian arteries, in their Jirst stage. Length. 

 The first stage of the left subclavian artery is 



much longer than that of the right, which it 

 exceeds by about the length of the Arteria 

 innominata. In the old subject, however, the 

 difference is scarcely so great, for at this 

 period of life, the part of the arch of the aorta, 

 from which the left subclavian artery arises, 

 is higher than that portion of it from which 

 the innominata springs. 



Position. The left subclavian artery is 

 nearer to the spinal column, the right to the 

 clavicle and sternum ; consequently the depth 

 of the artery from the surface is considerably 

 greater on the left side than on the right, a 

 circumstance which adds greatly to the diffi- 

 culty of the operation for securing the left 

 subclavian artery in a ligature. 



Direction. On. the left side, the artery in 

 its first stage runs almost vertically, but as it 

 approaches the scaleni, it inclines outwards 

 and forwards, in order to pass between these 

 muscles ; this latter part of the vessel is situ- 

 ated in the neck, and is the only portion of 

 its first stage found there. On the right side, 

 the subclavian artery runs nearly horizontally 

 outwards, and is placed throughout the whole 

 of its first stage within the limits of the antero- 

 inferior triangle of the neck; for although 

 somewhat concealed at its origin by the sterno- 

 clavicular articulation, yet it may be removed 

 from under cover of that joint, by extending 

 the neck, and depressing forcibly the shoulder 

 and clavicle. 



Relations. a. Pleura. The pleura is an 

 anterior relation of the commencement of the 

 left, but a posterior relation of the termina- 

 tion of the right subclavian artery. 



b. Veins. 1. The satellite vein of the right 

 subclavian artery, in its first stage (the right 

 vena innominata}, is parallel to the artery, 

 though on a plane anterior and inferior to it, 

 whilst the corresponding vein on the left side 

 crosses the left subclavian at right angles. 



2. The internal jugular vein runs parallel 

 to the left, but intersects at right angles the 

 front of the right subclavian artery. 



3. The vertebral vein is usually anterior to 

 the artery of the left, but posterior to the 

 artery of the right side. 



c. Nerves. The phrenic, vagi, and sympa- 

 thetic nerves are necessarily parallel to the left 

 subclavian artery, in the first stage of its course, 

 in consequence of its vertical direction, whilst 

 they run at right angles to the corresponding 

 part of the right, by reason of its transverse 

 course ; in other respects, however, these 

 nerves hold the same relative position to the 

 subclavian arteries at either side, the phrenic 

 and vagus being anterior, and the sympathetic 

 posterior, to the right and left subclavians 

 respectively. Lastly, the recurrent laryngeal 

 nerve passes behind the right subclavian artery, 

 looping round its under surface, whilst the 

 nerve on the left side encircles the arch of the 

 aorta, internal to the origin of the left sub- 

 clavian artery ; the recurrent is consequently 

 related to the inner side of the left subclavian 

 artery, but at no part of its course does it lie 

 posterior to that vessel. 



d. The thoracic duct and cesoj)hagus are 



