In the bend of the arm are three distinct veins, the _head_, _median_, and _basilican_. The ancients, before the discovery of the circulation of the blood, fancied the _head_, or upper vein, carried the blood from the head; the _median_, or middle, from the breast; and the _basilican_, from the liver, &c. but this idle conjecture is laid aside, as being highly absurd. When it is remembered what was said in the first Lecture, in Sect. V. of the circulation of the blood, it will then plainly appear, that all these veins become one before they enter the body; so that there can be no difference as to their quality in being opened: either therefore, which lays most conspicuously easy, is the vein that should be chosen; for the arms of people differ in this respect, as much as their features. In order to chuse therefore properly, examine with the finger how the veins lie; if upon a flat hard substance, it is a tendon; if a pulsation is perceived, there is an artery; both which ought to be avoided if there is a vein that lays more free and conspicuous to the sight and touch. If however it cannot be avoided, the vein ought to be opened with the greatest caution, for the pricking of a tendon would not only be exquisitely painful, but endanger the arm by inflammation, and even life itself; and the pricking of the artery would endanger the patient’s bleeding to death, or else form an _anauresma_, (which is a bag of blood protruding from the artery) equally dangerous to the life of the patient. In general the middle vein is the safest and most convenient, provided it does not cross the tendon: for the upper vein lies frequently very deep, and is but small, and the lower frequently crosses a tendon, or lies immediately over an artery. However, one or the other will frequently suit, and, with caution, the operation may be performed with ease. As to the choice of the arm, it can make no difference in regard to the effect, whether it is the right or left, for the veins of both arms end at last in the great trunk of the _vena cava_, before they enter the heart. To the operator, however, the right is the handiest, and to the patient, the left is most convenient. In that arm however where the best vein offers, that should be chosen. When the arm is fixed on, then tie it up. The place should be on the upper arm, about two inches from the bend, and the vein fixed on to be bled, first drawing up the skin a little, and laving on the ligature twice round the arm, drawn together with a draw knot; the reason of laying on the ligature above the intended orifice of the vein, is plain, as it stops the reflux of the blood, which is transfused from the heart by the arteries towards the fingers, from thence taken up by the veins, and by the ligature prevented from flowing back again, and consequently distends the veins, and swells them up.