ABNORMALITIES OF ARTERIES. 901 
THE ARTERIES OF THE UPPER LIMB. 
Subclavian Arteries.—The variations, so far as regards the origins of the subclavian 
arteries, have already been mentioned (p. 897). Other interesting modifications are met with in 
respect of its position and branches. 
The subclavian artery may rise as high as one or even one-and-a-half inches above the 
clavicle, though as a rule it does not reach higher than three-quarters of an inch above that 
bone. On the other hand, it may not rise even to the level of the upper border of the clavicle. 
These differences appear to be associated with the descent of the clavicle and sternum, which 
occurs as age Increases. 
The artery may pass in front of or through the scalenus anticus instead of behind it, or 
the vein may accompany it behind the muscle. 
The branches of the subclavian artery may be modified with reference to their points of origin ; 
thus those of the first part may be further in or out than usual, the suprascapular or some other 
branch of the thyroid axis may arise separately from the third part of the artery, and not 
uncommonly the posterior scapular artery is a branch of this part. The abnormalities of the 
vertebral branch have already heen described; those of the thyroid axis and its branches are 
numerous but not unportant. 
The internal mammary artery, usually a branch of the first part of the subclavian, is very 
variable as regards its origin. It may arise from the second or third parts, or from the thyroid 
axis, or it may spring from the aorta, or from the innominate or axillary arteries. All these 
variations are due to obliteration of the normal origin and the opening up of anastomoses. 
The internal mammary artery sometimes descends in front of the cartilages of one or more of 
the lower true ribs, and occasionally it gives off a large lateral branch (a. mamaria lateralis) 
which descends on the inner side of the chest wall nearly in the mid-axillary line, a point of 
importance in paracentesis. 
A few cases have also been noticed in which a bronchial artery has arisen from the internal 
mamuary. 
The superior intercostal branch of the subclavian may be absent. In any case its deep 
cervical branch may rise directly from the subclavian trunk. The superior intercostal is some- 
times formed from a postcostal instead of a precostal primitive channel, and in this case it passes 
between the necks of the ribs and the transverse processes of the vertebrae instead of, as usual, in 
front of the necks of the ribs. 
The axillary artery does not vary much as regards its origin or course. Its relations may be 
modified by the existence of a muscular or tendinous “axillary arch,” which, passing from the 
latissimus dorsi to the pectoralis major, crosses the lower part of the artery superficially ; and 
a further interesting modification is associated with an anomalous arrangement of its branches. 
Occasionally the sub-scapular, circumflex, and superior and inferior protunda arteries arise from 
the axillary by a common stem. In these cases the chief branches of the brachial plexus are 
grouped round the common stem instead of round the main trunk, and it is suggested that the 
common stem in question was originally the trunk artery of the upper limb, the lower part of 
which has been obliterated, the circulation being carried on by a vas aberrans which anastomoses 
below either with the brachial artery or with one of the arteries of the forearm. It is also 
said that a rudiment of this artery exists in a muscular branch which passes between the heads 
of the median nerve. 
Sometimes the axillary artery divides into the radial and war arteries, and more rarely the 
interosseous artery may spring from it. 
Obviously when the radial and ulnar arteries are formed by the division of the axillary, there 
is no brachial artery; its place is taken by the two abnormal vessels which, as a rule, are 
separated by the median nerve as they run through the upper arm; the radial is usually more 
superficial than the ulnar, and crosses outwards in front of it at the bend of the elbow. 
The brachial artery is rarely prolonged beyond its usual point of bifurcation, not uncommonly, 
however, it bifurcates at a higher level. Of the two terminal branches of the brachial, one may 
divide into radial and interosseous, the other forming the ulnar; or one may divide into radial 
and ulnar, whilst the other is the imterosseous artery. Occasionally the brachial artery ter- 
minates by dividing into three branches—viz. the radial, the ulnar, and the interosseous. In 
any case, the branch which gives origin to or becomes the interosseous was in all probability 
the original trunk. 
Division of the brachial artery at a higher level than usual occurs most commonly in the 
upper third of the arm, and least commonly in the lower third; the resulting trunks are often 
united near the bend of the elbow by a more or less oblique anastomosis. 
Tn cases of high division of the brachial artery the radial branch may pierce the deep fascia 
of the arm near the bend of the elbow, and descend in the forearm immediately beneath the 
skin; in other cases the radial runs deeper, and passes behind the tendon of the biceps. The 
war branch sometimes runs, on the internal intermuscular septum, towards the inner condyle, 
and then outwards towards the middle of the bend of the elbow under a band of fascia, from 
which the upper fibres of the pronator teres arise, or round the supracondylar process of the 
humerus if it is present. More commonly the ulnar branch descends towards the imner condyle, 
and crosses superficial to the flexor muscles or beneath the palmaris longus ; and in a few cases it 
is subcutaneous. Very occasionally the ulnar artery accompanies the ulnar nerve behind the 
inner condyle; in these cases it has obviously been fone by enlargement of the ordinary 
inferior profunda and posterior ulnar recurrent arteries. 
