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.