In the operation for tying the brachial artery, the known direction of the vessel, and the inner margin of the biceps muscle chiefly aid in determining its position. In consequence of the thinness of the parts which cover the artery, and the position of the basilic and median basilic veins, with respect to it. even the integuments must be divided with care.
After turning aside the superficial vein, should that be necessary, and dividing the fascia, the median nerve will probably come into view, and the artery will then be readily found. This is the course required under ordinary circumstances. But it may happen that after dividing the fascia it will be necessary to cut through a layer of muscular fibers in order to bring the artery into view. The influence of pressure with the finger in controlling the circulation, will enable the surgeon to determine if the vessel be behind the muscular fibers, and will guide him to the place at which they ought to be divided.
Again, as the brachial artery occasionally deviates from its accustomed place in the arm, it is prudent, before beginning an operation on the living body, to be assured of its position by the pulsation. Should the vessel be thus displaced, it has the ordinary coverings of the brachial artery, except at the lower part of the arm, where some fibers of the pronator teres will require to be divided in an operation for securing the vessel.
When the brachial artery is double, or when two arteries are present in the arm, both being usually placed close together, they are accessible in the same operation. The circumstance of one being placed over the fascia (should this very infrequent departure from the usual arrangement exist) will become manifest in the examination which ought to be made in all cases before an operation is begun. And, as regards the occasional position of one of the two arteries be- neath a stratum of muscular fibers, or its removal to the inner side of the arm (in a line towards the inner condyle of the humerus) it need only be added that a knowledge of these exceptional cases will at once suggest the precautions which are necessary, and the steps which should be taken when they are met with. — The foregoing observations have reference to operations on the brachial artery above the bend of the elbow ; the surgical anatomy of the vessel opposite that joint requires a separate notice.
At the bend of the elbow the disposition of the brachial artery is chiefly, or, at least, most commonly, of interest in a surgical point of view, because of its connection with the veins from which blood is usually drawn in the treatment of disease. The vein (median basilic) which is generally the most prominent and apparently best suited for " venesection" is commonly placed over the course of the brachial artery, separated from it only by a thin layer of fibrous structure (the expansion from the tendon of the biceps muscle) ; and under such circumstances, it ought not, if it can be avoided, to be opened with a lancet, except in a part which is not contiguous to the artery.
If two arteries are present, instead of the ordinary single trunk, they are commonly close together ; but it now and then happens that an interval exists be- tween them — one being in the usual situation of the brachial, the other nearer, in different degrees in different cases, to the inner condyle of the humerus. There is on this account an additional reason for precaution when venesection is to be performed ; and care is the more necessary as the second artery may be immediately under the vein without the interposition of fascia.
From Quain's Anatomy.