776 HUMAN ANATOMY. 



Comparative anatomy and embryology both indicate that the occurrence of a well-devel- 

 oped superficial brachial, continuous below with the radial, is the primary condition, and that 

 the origin of the radial as a terminal branch of the brachial proper is a secondary condition, 

 due to an anastomosis between the lower part of the original superficial stem and the brachial 

 and to the subsequent diminution or partial obliteration of the former above this anastomosis 

 (Fig. 74S i:-). 



Another branch, normally present but usually insignificant, which may reach an extraor- 

 dinary development, is the a. pliccs cubiti superficialis. It arises from the lower portion of the 

 brachial and, passing inward and downward beneath the tendon of the biceps, is distributed to 

 the flexor carpi radialis and the palmaris longus. When abnormally developed, it forms what 

 has been termed the accessory ulnar artery, and passes down the forearm, immediately beneath 

 the deep fascia and between the two muscles just mentioned, and terminates by anasto- 

 mosing with the ulnar, or in some cases replaces it and enters into the formation of the palmar 

 arches. 



Supernumerary branches accessory to the branches usually present may also occur, and, 

 in addition, the brachial may give rise, in its upper part, to the subscapular and the posterior 

 circumflex, normally branches of the axillary ; in its lower part, to the radial recurrent; and, at 

 its bifurcation, to the interosseous artery or to the median, which is usually a branch of the 

 interosseous. 



Practical Considerations. — Spontaneous aneurism of the brachial artery is 

 rare, and is usually associated with marked arterio-sclerosis or vi'ith cardiac disease. 

 Wounds and traumatic aneurism are common, though lessened in frequency by the 

 protected position of the upper two-thirds of the artery on the inner side of the arm. 

 Aneurism has, however, followed a stab-wound from the outer side, which, after 

 passing through the biceps, involved the vessel. Arterio-venous aneurism just 

 above the bend of the elbow was formerly often met with as a result of the accidental 

 wounding of the artery during phlebotomy of the median basilic vein, parallel with 

 the vessel at that point and. separated from it only by the lacertus fibrosus. 



The line of the artery is from the junction of the anterior and middle thirds of 

 the axilla to the middle of the bend of the elbow when the arm is abducted and the 

 forearm extended and supinated. 



The artery in the upper two-thirds of its course may be cornpressed against the 

 inner side of the humerus by pressure directed outward and a very little backward 

 along the internal border of the coraco-brachialis and biceps. This muscular border 

 may be visible, or may be recognized by picking it up between the thumb and finger. 

 The artery may be overlapped by this inner edge of the biceps, especially in mus- 

 cular subjects. At the middle of the arm, over the insertion of the coraco-brachialis 

 into the flat surface above the beginning of the internal supracondyloid ridge, it may 

 most easily be subjected to compression. In the lower third the pressure must be 

 directed backward, as the humerus — separated from it by the brachialis anticus 

 muscle — then lies behind it. 



Ligatio7i of the vessel at its upper third is effected through an incision made 

 along the inner border of the muscular ridge of the coraco-brachialis muscle, the 

 fibres of which may with advantage be exposed and identified. Nothing lies between 

 the artery and the muscle except the median nerve. The basilic vein is to the inner 

 side of the vessel and may, before the incision is made, be identified and avoided by 

 compression of the axillary vein above. The ulnar nerve also lies to the ifiner side. 

 The needle may be passed in either direction. 



In ligation at the middle of the arm, the limb should be abducted with the elbow 

 slightly flexed, and should be supported by an assistant. If the arm is allowed to 

 rest upon a flat surface, the triceps is pushed upward and may be mistaken for 

 the biceps, and the dissection may bring into view the inferior profunda artery 

 and the uln^ar nerve instead of the brachial and the median (Heath). It is well 

 to see and identify the innermost fibres of the biceps. After they are displaced 

 outward, the median nerve (beginning to bear to the inner side) should be separated 

 from the vessel, the sheath opened, the venae comites (the inner of which is usually 

 the larger) drawn aside, and the needle passed from the nerve. Jacobson calls 

 attention to the fact that this usually easy ligation may be difficult when the artery 

 is concealed by the median nerve at the point at which it is sought, and when its 

 calibre is small and its beat feeble as the result of hemorrhage. The median nerve 

 (from transmitted pulsation), the inferior profunda artery, and even the basilic vein 

 have been mistaken for the brachial. 



