Lastly, the structures to be divided or put aside in order to expose the artery are,-1. the skin; 2. the subcutaneous cellular stratum; 3. the superficial lamina of the fascia lata, forming the anterior wall of the sheath of the sartorius; 4. the sartorius itself; 5. the deep lamina of the fascia forming the posterior wall of the sheath of the sartorius, and the anterior wall of the femoral canal ; and, 6. the proper sheath of the vessels.
The difference between the anatomical re lations of the operation in the middle and inferior stages of the artery depends upon the modifications to be observed in the relations of the vessel at the two points, and also in some of the parts concerned. The number and order of the structures interposed between the surface and the artery are the same as in the third, but their disposition and relations differ in some important particulars so much as to authorize a difference in the proceedings to be adopted, and to justify a preference in favour of the former. I. The artery is nearer to the anterior surface of the limb, and the more so the nearer to the commencement of the stage: it is therefore more easily reached and in the same proportion. 2. It is nearer to the inner than the outer margin of the sar torius, and, in like manner, the more so, the nearer to its upper extremity; and hence it may be brought into view with more ease and with less disturbance of the muscle by dis placing its inner margin outward, than its outer inward.
The latter proceeding is advocated by Hut chison for the purpose of avoiding the sa phena vein and the lymphatics. That the vein will be effectually secured from danger by cutting upon the outside of the sartorius will be at once admitted ; but it appears to the author that the advantage contemplated will be more than counterbalanced by the dis advantages attending it, and on the other hand that the proceeding is not necessary : for, I. if the outer margin of the muscle be cut upon in the middle of the vessel, the incision must be made considerably external to the line of the artery's course, and thereby the guide to the vessel otherwise afforded by that line must be lost, and uncertainty and consequently embarrassment be likely to ensue in seeking for the artery after having displaced the muscle. 2. Much more disturbance and violence are likely to be inflicted upon the artery and the adjoining parts by the plan in question, in asmuch as the vessel is so much nearer to the inner than the outer margin of the muscle ; in consequence of which the muscle must be displaced to a much greater extent in proceed ing from without inward, and the obstruction offered by it to the performance of the other steps of the operation must lead to greater violence either to the artery or to the muscle ; and afterward a valvular wound must be left, a circumstance very unfavourable in the event of the occurrence of inflammation and sup puration in the vicinity of the track of the vessel, and those objections are the stronger because the artery is usually sought at the upper part of the stage, where it is but little overlapped by the muscle. On the other hand
the saphena vein ought not to be endangered in the operation, for it is situate so far internal to the artery that the incision ought not to fall upon it. The case is different from that of cut ting upon the inner margin of the sartorius during the third stage of the vessel ; for there the vein is for the most part close to the edge of the muscle, and the wound must be in clined in depth from within outward, by which direction the vein is interposed between the surface and the artery; whereas, in the second stage, whether the operator, in proceeding by the inner margin of the muscle, cut directly upon the artery's course or upon the edge of the sartorius, there is sufficient space between it and the vein to leave the latter safe. The course of the artery may be crossed at any part by time superficial femoral veins, as has been explained, and they, if they present, will be in danger of division ; but this inconvenience would not be removed by the plan in question, whereas both it and the danger to the saphena may be avoided by an easier and less ob jectionable proceeding than that of cutting upon the outer edge of the sartorius, viz. 1. by ascertaining, through means of pressure, the situation and course of the veins; and, 2. by proceeding with somewhat more caution, where there is reason to expect their presence, dividing first only the skin and continuing the incision through the subcutaneous structure, not by a single stroke, by which the vein if in the way must necessarily be divided, but gra dually, until the vessel has been exposed and drawn aside. It seems therefore to the author not only unnecessary, but very objectionable to cut upon the outer margin of the sartorius, in exposing the femoral artery above the mid dle of the thigh. 3. The anterior wall of the femoral canal is much thinner than in the third stage, and therefore more easily ma naged. 4. The vein is directly behind the artery, and thereforg the needle may be passed with equal safety from either side, according to circumstances : in operating by the inner margin of the sartorius it will be more easily done from the inside : the position of the vein and its close connection to the artery render it especially necessary that the extremity of the needle be kept in contact with the artery in being carried behind it. The saphenus nerve requires the same attention as in the third stage.