

BracJiial Plexus 249 



considerably abducted and the relaxed tissues allowed the fingers to 

 be thrust high into the space. 



In enucleating glands which have become implicated in scirrhus 

 mammas the surgeon employs his fingers, not his scalpel, lest he 

 wound the large vessels ; but in tearing them out he runs the risk of 

 rooting a little alar thoracic artery from the main vessel. He must 

 proceed with very great care when removing glands from the outer 

 part of the space. 



In the case of scirrhus mammae the surgeon cannot be sure that 

 there is no secondary implication of the glands until he has opened 

 up the fascia of the floor of the axilla and introduced his finger. It is 

 advisable, therefore, in every case of malignant disease to prolong the 

 incision into the arm-pit in the search for implicated glands. 



The axillary glands are associated beneath the clavicle with those 

 at the root of the neck. When, therefore, the surgeon is considering 

 the advisability of operating in mammary cancer he should carefully 

 examine the supra-clavicular region as well as the arm-pit. 



THE BRACHIAL PLEXUS 



The brachial plexus is formed by the anterior divisions of the 

 fifth, sixth, seventh, and eighth cervical nerves, and by the chief part 

 of that of the first dorsal, which has come up in front of the neck 

 of the first rib. Resting in the grooves on the transverse processes of 

 the lower cervical vertebrae, the nerves emerge between the anterior 

 and middle scalene muscles, which arise from the anterior and posterior 

 tubercles of those processes, respectively. The subclavian artery also 

 lies behind the anterior and in front of the middle scalene : the plexus 

 is, thus, chiefly above the artery in the second and third portions of its 

 course, but the lowest strand of the plexus is partly behind it. In this 

 relative position the plexus and the artery descend beneath the cla- 

 vicle and the subclavius muscle into the axilla. 



The anterior divisions of the fifth and sixth nerves join to form a 

 single cord, as do also the divisions of the eighth cervical and the first 

 dorsal, the division of the seventh passing on by itself. 



On the outer side of the scalenus medius each of these three large 

 bundles splits into an anterior and posterior trunk, of which the anterior 

 trunks of the upper and middle unite to form the outer cord of the plexus. 

 The lower anterior trunk runs on independently as the inner cord, whilst 

 the posterior cord is formed, as might be anticipated, by the union of all 

 three posterior trunks. 



In the top of the arm-pit these cords lie above the axillary artery ; 

 behind the pectoralis minor they lie, as their names express, one to the 

 outer side, one to the inner side of the vessel, and one behind it ; and 

 in the third part of the course of the artery they are breaking into their 

 terminal branches. 



