SSO THE SUBCLAVIAX ARTERY. 



and rests between the scalenus auticus and scalenus medius muscles on 

 the first rib. At the outer border of the first rib it ceases to be called 

 subclavian, and is continued into the axillary artery. 



Each subclavian artery is conveniently divided into three parts, — the 

 first part extending from the origin of tlie vessel to the inner border of 

 the anterior scalenus muscle ; the second consisting of the portion of the 

 vessel situated behind that muscle ; and the tJiird reaching outwards 

 to the external border of the first rib. In examining each of these 

 portions ia detail, it will be necessary in the first part to give separate 

 descriptions for the right and the left sides, as there is a material 

 difference in the origin, course, and relations of the two vessels. 



THE FIRST PART OF THE RIGHT SUBCLAVIAN ARTERY COmnieUCeS close 



to the trachea, at the division of the innominate arterj', behind the upper 

 part of the sterno-clavicular articulation, and ends at the inner margin 

 of the anterior scalenus muscle. Separating from the carotid artery, it 

 arches upwards and outwards, and ascends above the level of the clavicle 

 to an extent which varies in different cases. It is deeply placed, being 

 covered by the platysma, the sterno-mastoid, the sterno-hyoid, and 

 fiterno-thyroid muscles, and tlie deep cervical fascia. It is in contact 

 witli the pleura inferiorly, and is separated by an interval from the 

 longus colh muscle behind. 



Eelafioii to Vems. — The siihdavkm vein lies lower than the arter}', 

 close under the clavicle. In its course to joiu this vein, the internal 

 jugular passes in front of the artery near the scalenus muscle, as do 

 also, nearer the middle line, the anterior jufjular and verteJjral veins. 



Relation to Nerves. — The vagus nerve passes in front of the artery 

 on the inner side of the internal jugular vein, and its recurrent laryngeal 

 branch, turning round below the artery, ascends behind. Some cardiac 

 branches of the sgmpathetlc nerve pass down over the artery, while the 

 main trunk passes behind. 



THE FIRST PART OF THE LEFT SUBCLAVIAN ARTERY ariseS from the 



upper surface of the arch of the aorta, at the left end of its transverse 

 portion, and ascends to the margin of the first rib, behind the insertion 

 of the anterior scalenus muscle. It is, therefore, longer than the first 

 part of the right subclavian, and ascends at first almost vertically out 

 of the chest, instead of arching, like that vessel, outwards across the 

 neck. It is at first overlapped b}' the left lung, and is covered in front 

 and on the left side by the pleura ; it rests on the longus colli muscle, 

 and lies, for a short space, in front of the oesophagus (here deviating to 

 the left side), and the thoracic duct. To the inner or right side of the 

 vessel are situated the left carotid artery and the trachea, and further 

 up the oesophagus and the thoracic duct. 



Relation to Few^s.— The internal jugular vein is immediately before 

 the artery, where it turns outwards from the thorax, close to the scalenus 

 muscle ; and the left innominate vein is likewise anterior to it. 



Relation to Nerves. — The jmeumogastric nerve is anterior to the first 

 part of the left subclavian artery, and parallel with it, the recurrent 

 branch on this side turning round below the arch of the aorta. The 

 fhrcnic nerve descends over the artery along the inner margin of the 

 scalenus muscle, immediately outside the thyroid axis. The cardiac 

 nerves of the left side, descending from the neck, are close to the 

 artery. 



THE SECOND PART OF THE SUBCLAVIAN ARTERY, the short portion COU- 



