Here then, the shoulder being in this position, and the arm held by the side, the measurement commences, and the fixed point chosen on each side of the immediate subject operation are the two ends of the clavicle; as nearly between these as can be done, consistently with keeping quite clear of the bone, a line must be drawn superior and internal to it, and the given number of proportional parts, into which this line must be divided, are seven in number both in the male and female; and now the situation of the artery may be most accurately indicated as being undeviatingly three of these proportional parts distant from the inner, and four from the outer end of the clavicle; in consequence of which, if a fine instrument, held at right angles to the clavicle, were directed downward and inward, it would at 1 and ¼ of the above mentioned parts from the surface of the clavicle, reach the artery, and being pushed farther, would pass through it. This is an absolute demonstration of the precision and ease attending the principle I have announced, and of its applicability even to the most difficult of all operations. In order, however, to perform the operation throughout, the point which I have indicated must be the center of an incision through the integuments made in the line above mentioned, and must extend at least two parts inward and two outward from the central point. Over the Trapezius outward, and over the clavicular attachment of the Sterno-cleido-mastoid muscle inward, it is not adviseable to cut deeper than the integuments, which sufficiently relieves the hand of the operator, without the present execrable practice of dividing the last mentioned muscle, which is not only unnecessary, but highly faulty, as this attachment serves as one of those particular points, above alluded to, incidental to certain operations, which, by means of its edge, kept lax during the operation, very nearly directs the knife to a small protuberance on the superior anterior surface of the first rib to which the scalenus primus is attached, and immediately external to which the artery itself lies. Above all, the incision ought to be cautiously continued on the inner side, in order to avoid the large veins situate there; various branches of these veins may come in the way, and the more considerable may be easily avoided, but if not, they may be tyed. In continuing the incision inward and downward, an ascending branch of the vein is in the way, which, when it is considerable, may also, previous to the continuance of the incision, be tyed. The incision itself, as you pass inward, must be very limited indeed, as the jugular vein is internal to it; and external to it there is a twig of the brachial nerve, both of which are much exposed to injury.