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38 COMMENTARY ON PLATES 15 & 16.

In the lower third of the arm it is not likely that the opera­tor will encounter the ulnar nerve, and mistake it for the median, since the former, d, Plate 16, is consider­ably removed from the vessel. If the incision be made precisely in the usual course of the brachial artery, the ulnar nerve will not show itself. It will be well, however, to bear in mind the possible occurrence of some of those anomalies to that normal relative posi­tion of the artery, the median, and the ulnar nerve, which the accompanying Plates represent.

The median nerve, D, Plate 16, is sometimes found to lie beneath the artery in the middle and lower third of the arm. At other times it is found far removed to the inner side of the usual position of the vessel, and lying in close contact with the ulnar nerve, d. Or the brachial artery may take this latter position, while the median nerve stands alone at the position of D, Plate 16. Or both the main artery and the me­dian nerve may course much to the inner side of the biceps muscle, A, Plate 16, while in the usual situation of the nerve and vessel there is only to be found a small arterial branch (the radial), which springs from the brachial, high up in the arm. Or the nerve and vessel may be lying concealed beneath a slip of the brachialis anticus muscle, E, Plate 16, in which case no appearance of them will be at all manifested through the usual place of incision made for the liga­ture of the brachial vessel. Or, lastly, there may be found more arteries than the single main brachial ap­pearing at this place in the arm, and such condition of a plurality of vessels occurs in consequence of a high division of the brachial artery. Each of these variations from the normal type is more or less fre­quent; and though it certainly is of practical import to bear them in mind, still, as we never can foretell their occurrence by a superficial examination of the limb, or pronounce them to be present till we actually encounter them in operation, it is only when we find them that we commence to reason upon the facts; but even at this crisis the knowledge of their anatomy may prevent a confusion of ideas.

That generalization of the facts of such anomalies as are liable to occur to the normal character of the brachial artery, represented in Plates 15 and 16, which appears to me as being most inclusive of all their various conditions, is this--viz., that the point of division into radial, ulnar, and interosseous, which F, Plate 16, usually marks, may take place at any part of the member between the bend of the elbow and the cora­coid process in the axillary space.

At the bend of the elbow, the brachial artery usual­ly occupies the middle point between e, the inner condyle of the humerus and the external margin of the supinator radii longus muscle, G. The structures which overlie the arterial vessel, C, Plate 16, at this locality, numbering them from its own depth to the cutaneous surface, are these--viz., some adipose cel­lular membrane envelopes the vessel, as it lies on E, the brachialis anticus muscle, and between the two accompanying veins; at the inner side of the artery, but separated from it by a small interval occupied by one of the veins, is situated the median nerve d, Plate 15. Above all three structures is stretched that dense fibrous band of the fascia, H, Plate 16, which becomes incorporated with the common fascial covering of the forearm. Over this fascial process lies the median basilic vein, F B, Plate 15, accompanying which are seen some branches of the internal cutaneous nerve. The subcutaneous adipose tissue and common integu­ment cover these latter. If it be required to ligature the artery at this locality, an incision two inches and a half in length, made along the course of the vessel, and avoiding the superficial veins, will expose the fas­cia; and this being next divided on the director, the artery will be exposed resting on the brachialis anti­cus, and between the biceps tendon and pronator teres muscle. As this latter muscle differs in width in seve­ral individuals, sometimes lying in close contact with the artery, and at other times leaving a considerable interval between the vessel and itself, its outer mar­gin is not, therefore, to be taken as a sure guide to the artery. The inner border of the biceps indicates much more generally the situation of the vessel.

The bend of the elbow being that locality where the operation of phlebotomy is generally performed, it is therefore required to take exact account of the struc­tures which occupy this region, and more especially the relation which the superficial veins hold to the deeper seated artery.

COMMENTARY ON PLATES 15 & 16. 39

In Plate 15, the artery, C, is shown in its situation beneath the fascial aponeurosis, which comes off from the tendon of the biceps, a por­tion of which has been cut away; and the venous vessel, F B, which usually occupies the track of the artery, is pushed a little to the inner side. While opening any part of the vessel, F B, which overlies the artery, it is necessary to proceed with caution, as well because of the fact that between the artery, C, and the vein, F B, the fascia alone intervenes, as also because the ulnar artery is given off rather frequently from the main vessel at this situation, and passes superficial to the fascia and flexors of the forearm, to gain its usual po­sition at K, Plate 15. I have met with a well marked example of this occurrence in the living subject.

The cephalic vein, D, is accompanied by the exter­nal cutaneous nerve, which branches over the fascia on the outer border of the forearm. The basilic vein, B, is accompanied by the internal cutaneous nerve, which branches in a similar way over the fascia of the inner and fore part of the forearm. The numerous branches of both these nerves interlace with the super­ficial veins, and are liable to be cut when these veins are being punctured. Though the median basilic, F, and the basilic vein, B, are those generally chosen in the performance of the operation of bleeding, it will be seen, in Plate 15, that their contiguity to the arte­ry necessarily demands more care and precision in that operation executed upon them, than if D, the cephalic vein, far removed as it is from the course of the artery, were the seat of phlebotomy.

As it is required, in order to distend the superficial veins, D, B, F, that a band should be passed around the limb at some locality between them and the heart, so that they may yield a free flow of blood on puncture, a moderate pressure will be all that is needful for that end. It is a fact worthy of notice, that the excessive pressure of the ligaturing band around the limb at A B, Plate 15, will produce the same effect upon the veins near F, as if the pressure were defective, for in the for­mer case the ligature will obstruct the flow of blood through the artery; and the vein, F, will hence be un­distended by the recurrent blood, just as when, in the latter case, the ligature, making too feeble a pressure on the vein, B, will not obstruct its current in that degree necessary to distend the vessel, F.

Whichever be the vein chosen for phlebotomy at the bend of the elbow, it will be seen, from an exam­ination of Plates 15 and 16, that the opening may be made with most advantage according to the longitudi­nal axis of the vessel; for the vessel while being cut open in this direction, is less likely to swerve from the point of the lancet than if it were to be incised across, which latter mode is also far more liable to implicate the artery. Besides, as the nerves course along the veins from above downwards--making, with each other, and with the vessels, but very acute angles--­all incisions made longitudinally in these vessels, will not be so likely to divide any of these nerves as when the instrument is directed to cut crossways.

The brachial artery usually divides, at the bend of the elbow, into the radial, the ulnar, and the interos­seous branches. The point F, Plate 16, is the com­mon place of division, and this will be seen in the Plate to be somewhat below the level of the inner condyle, e. From that place, where the radial and ulnar arte­ries spring, these vessels traverse the forearm, in gene­ral under cover of the muscles and fascia, but occasion­ally superficial to both these structures. The radial artery, F N, Plate 16, takes a comparatively superficial course along the radial border of the forearm, and is accompanied, for the upper two-thirds of its length, by the radial branch of the musculo-spiral nerve, seen in Plate 16, at the outer side of the vessel. The supinator radii longus muscle in general overlaps, with its inner border, both the radial artery and nerve. At the situ­ation of the radial pulse, I, Plate 15, the artery is not accompanied by the nerve, for this latter will be seen, in plate 16, to pass outward, under the tendon of the supinator muscle, to the integuments.

The ulnar artery, whose origin is seen near F, Plate 16, passes deeply beneath the superficial flexor mus­cles, L M K, and the pronator teres, I, and first emerges from under cover of these at the point O, from which point to S, Plate 16, the artery may be felt, in the liv­ing body, obscurely beating as the ulnar pulse. On the inner border of the ulnar artery, and in close connexion with it, the ulnar nerve may be seen looped round by small branches of the vessel.