THE AXILLARY ARTERY. 431 



On the right side, though deeply placed and closely connected with important parts, the 

 first division of the subclavian artery may be tied in the interval between the common carotid 

 artery and the internal jugular vein without extreme difficulty. But inasmuch as the distance 

 between the bifurcation of the innominate on the one hand, and the origin of the vertebral 

 artery on the other, seldom measures more than an inch, and is often much less, the success 

 of the operation is exceedingly doubtful. 



In order to place a ligature on the portion of the right subclavian artery here referred to, 

 it is necessary to divide the three muscles which cover it, together with the layers of fascia 

 between and beneath them. In doing this the anterior jugular vein must be avoided, and the 

 suprastemal branch of the suprascapular artery will probably require to be secured. In the 

 farther steps of the operation, the exact relations of the artery to the internal jugular, 

 vertebral and innominate veins, the pneumo-gastric nerve with its recurrent branch, and the 

 pleura, are to be well kept in view. 



It is to be remembered also that the first part of the right subclavian artery is occasionally 

 more deeply placed than usual ; as in those cases in which it springs from the back part of 

 the aortic arch, or, more frequently, when it merely separates from the innominate behind 

 the carotid. 



The circulation in the subclavian artery may be arrested by pressure directed backwards 

 and downwards in the supraclavicular fossa, so as to compress the third part of the vessel 

 against the subjacent first rib. 



Collateral circulation. After ligature of the third part of the subclavian artery, blood is 

 supplied to the upper limb through the anastomoses upon the scapula between the supra- 

 scapular, posterior scapular and subscapular arteries, and those formed by branches of the 

 internal mammary and intercostal arteries with the thoracic branches of the axillary artery. 

 After ligature of the first part of the artery, blood is conveyed to the distal portion of the 

 trunk mainly by the vertebral artery, to a less extent by the inferior thyroid, internal 

 mammary and superior intercostal arteries : the axillary artery receives blood also through 

 the anastomoses formed by its thoracic branches, and the fore part of the thoracic wall is 

 supplied by the intercostal and epigastric arteries. 



AXILLAEY ARTERY (I). 



The axillary artery is that part of the artery of the upper limb which extends 

 from the outer border of the first rib to the lower margin of the teres major muscle. 

 In this course it passes through the axilla, lying to the inner side of the shoulder- 

 joint and upper part of the humerus, and its direction varies with the position of 

 the limb, being curved downwards or upwards, or being straight, according as the 

 arm hangs by the side, or is elevated to a greater or less degree. With the arm 

 raised to the level of the shoulder, a line drawn from the most prominent part of 

 the clavicle to the inner side of the eminence formed by the biceps and coraco- 

 brachialis muscles will indicate the position of the vessel. 



The axillary artery is crossed in front by the pectoralis minor muscle, and is 

 thus conveniently divided into three parts : the first part lies above the pectoralis 

 minor and is about one inch long ; the second part, placed behind that muscle, is 

 somewhat longer ; and the third part, beyond it, is rather over three inches in 

 length. 



In the FIRST PART of its course the artery is deeply placed, being covered by the 

 pectoralis major, by a quantity of areolar and fatty tissue, and by a prolongation of 

 the costo-coracoid membrane, as well as by the lower part of the subclavius muscle 

 when the shoulder is depressed. This part of the artery is also invested by the 

 axillary sheath, a membranous structure continued downwards from the deep 

 cervical fascia (p. 298) and surrounding both the trunks of the vessels and the 

 brachial plexus of nerves. It rests upon the first intercostal space and the first 

 digitation of the serratus magnus. The axillary vein lies to the inner side and 

 somewhat in front of the artery, and the cephalic, and acromio-thoracic veins cross it 

 to reach the main trunk. The nerves of the brachial plexus are to the outer side, 

 the external anterior thoracic nerve crosses in front, and the internal anterior thoracic 

 and posterior thoracic nerves pass behind it. 



In the SECOND PART of its course the artery is covered in front by the pectoralis 



