Varieties of the radial and ulnar arteries. — The size of these vessels, together with the comparative exposure to mechanical injury which their situation involves, renders an exact knowledge of their distribution abso lutely essential to the surgery of the upper extremity ; and the same causes also require that the more important varieties, which con stitute so large a per centage of their actual numbers, should at least experience some consideration. In sketching out a few of these it is impossible to avoid ac6knowledging great obligations to Mr. Quain's recent work, " The Anatomy of the Arteries," in which the number of subjects, which serve as the groundwork of the estimates, the evident care with which they have been examined, and the beauty of the illustrations, leave little to be wished for. • Varieties of origin. —Rarely does either of the two vessels arise from the brachial at a point lower than the ordinary situation op posite the coronoid process of the ulna : a higher division of this artery, or as it is called, a " high origin" of one of these its branches, is, on the contrary, by no means an uncommon occurrence, It is worthy of notice, that in the majority of these cases, there is no lateral correspondence of the variety,— in the op posite limb the distribution is the usual one.
The most frequent of the tvvo is the high origin of the radial, which may cotne off' from the axillary, or from the brachial artery in any part of its course. In this case, the remaining trunk, although directly continuous with the ulnar artery, and lacking the usual means of distinction from it, bears yet the name of brachial, since it generally possesses the ordi nary relations and distribution of the latter vessel. Under these circumstances, the radial passes down the arm from the place where it is given off, generally lying rather close to the brachial, and on its outer side, until it reaches the forearm ; subsequently it preserves its usual arrangement and termination. But though, for the most part, its course is thus only altered by the possession of an additional por tion in the upper arm, this irregularity is some thnes associated with another which concerns its course, viz. a position of the artery super ficial to the fa' scia ; and here it would often have a close juxtaposition to the:median basilic vein.at the bend of the elbow, which careless ness in venmsection might render dangerous or even fatal. A similar deviation may obtain in the remainder of its course, placing it super ficially to the supinator radii longus, instead of beneath its overlapping inner border ; or causing it to cross over the extensor tendons at the wrist instead of under them. The latter variety is frequently associated with another alteration in the course of the vessel, which, after giving off the superficialis volm at a point much higher than usual, immedi ately turns round the outer border of the forearm, so as to leave this small branch alone occupying its ordinary position at the wrist. Other °deviations are comparatively
rare :—thus occasionally the vessel enters the palm in the second instead of the first inter osseous space.
Variations in its distribution appear chiefly dependent on its relative size. If smaller than usual, a kind of enlarged communicans ulnm reinforces its deep palmar arch, or gives off its radialis indicis and magna pollicis branches ; or the compensative stream may arrive by another channel, viz., a dilated anterior inter osseous to join the artery as it turns round the swrist; or by a large posterior branch of the same vessel which meets it juSt before entering the metacarpal interspace. Where, as is by no means infrequent, the radial is larger than ordinary, its increased size is prin cipally expended in supplying, through a large superficialis volm artery*, one or more of the outer digital branches which usually come from the superficial palmar arch: or, by means of a dorsal metacarpal of unusual magnitude, digital branches to the opposed sides of the index and middle fingers.
The high origin of the ulnar is contrasted with that of the radial in another respect beside that of its lesser frequency, since it is almost always conjoined with an important difference in the situation of the vessel in the forearm, which lies superficial to the flexors ordinarily covering it, and immediately beneath the fascia :— sometimes it is even sub-cutaneous. Its course is also somewhat affected by this origin, the vessel approaching the inner side of the forearm at a higher point than usual: in other cases, however, it possesses almost a median position during the greater part of this region, and only turns inwards to its ordinary distribution near the wrist.
In size, the ulnar artery is more frequently diminished than increased by variations. The decrease is compensated sometimes by a radial vessel supplying one or more of its digital branches or contributing to its palmar arch : at others, its long branch which accompanies the median nerve is enlarged to a vessel of considerable size, which similarly assists it ; while, in a few instances, the dilated anterior interosseous has an analogous termination.
The origin of the interosseous artery is subject to some variation, being liable to occur as a divarication from the radial or brachial, or though rarely —from the axillary : its en largement aids a deficient radial or ulnar vessel, just as its diminutive size is supplied by them.