The most common irregularity of the brachial artery is a high bifurcation into the ulnar and radial. This may occur in any part of its course. In this case the ulnar and radial arteries, having arrived in the fore-arm, may pursue their usual course; or the radial may, in certain cases, run superficially, or the ulnar may be the superficial branch: usually, however, in these irregularities, the ulnar follows the ordinary deep course of the brachial artery. Mr. Burns observes, that, when the ulnar is the anomalous branch, the bifurcation usually takes place higher up than when the radial is irregular.

In the high bifurcation, the radial artery usually lies at first on the inside, and afterwards crosses the ulnar, or continued trunk, to become external. These two vessels may be connected in their course by a transverse branch; and the transverse branch may give off a median artery, which descends on the front of the fore-arm in company with the median vein: in other cases, the median artery may come from the brachial, radial, or ulnar: it usually terminates in the superficial palmar arch, sometimes in the deep one.

Dr. Quain mentions a remarkable instance, in which the brachial artery divided into two branches, and, lower down, reunited to form a single trunk, which afterwards bifurcated regularly into the radial and ulnar.* A similar instance is recorded by Professor Quain ;† and a preparation of the same kind of irregularity exists in the Macartney collection in the Anatomical Museum of the University of Cambridge. Mr. Norton, of the Royal Liverpool Institution, has met with a similar case. Dr. Geddings, of Maryland, in speaking of the varieties of the brachial artery, observes, " In some instances the radial and ulnar arteries, after separating high in the arm, or axilla, pass for a limited distance down the arm, and then unite." He gives no reference, however, but may possibly allude to the following passage in the work of Dr. Green, who is quite explicit on the subject:—"Sometimes the axillary artery divides into two vessels which again unite at the fold of the arm, so that there are in reality two brachial arteries lying close to one another, and of equal magnitude. I have seen two striking examples of this kind. In one case, the brachial divided into two branches, which in like manner conjoined above the fold of the arm."*

* Elements of Anatomy, 4th edition, p. 558.

† Anatomy of the Arteries of the Human Body, p. 221.

In three cases out of forty, Professor Harrison found " a small branch arising from the upper part of the brachial and descending to the elbow, where it joined the radial artery; in two instances this superficial branch descended in the forearm beneath the superficial flexors, and was distributed to the muscles in this region; and in two cases it accompanied the brachial nerve beneath the annular ligament of the carpus, and joined the superficial palmar arch of arteries."† These have been described under the name of " vasa aberrantia:" they are frequently of considerable size.

The next variety to be noticed is that of the brachial artery giving off the interosseal: a case of this kind has been observed by Dr. Flood in the Richmond Hospital School. In some rare cases the brachial artery divides at one point into three branches, viz., the radial, ulnar, and interosseous.