It is to be borne in mind that, in determin ing the direction of the vessel's course, the limb must be placed in the bearing which it holds naturally in the erect posture, inasmuch as an inclination to either side will influence materially the direction of the artery : thus an inclination of the limb inward will at once give it the same tendency, and render it spiral, both which conditions are removed by placing the limb in its ordinary position.
In consequence of the course which the vessel pursues, and of the oblique position of the femur conjointly, the femoral and popliteal arteries hold very different relations to the shaft of that bone ; the former, in the first stage of its course, being in a plane anterior to the femur, and in the middle of the limb being upon its inside; while the latter is situate be hind the bone, and at the inferior part of the popliteal region corresponds to the axis of its shaft : hence the artery is said" to pass some what in a spiral manner in reference to the thigh bone; but this is incorrect, the spiral course being only apparent and resulting from the combined effect of the obliquity of the artery itself backward and outward, and of the shaft of the femur inward and forward : that this is so may be satisfactorily shewn by the application of the plumb-line to the course of the artery, upon the different aspects of the limb; from which it will appear that, allow ance being made for the serpentine deviations already adverted to, the general course of the vessel is, gum pro.rim?, straight, and that it cannot, at all with propriety, he said to be spiral, this being not a real but an apparent direction, the result of the circumstances which have been mentioned.
The point at which the femoral artery com mences is referred by most writers to Ponpart's ligament; this method of demarcation is at tended with the inconvenience, that during life the exact situation of the ligament is difficult to determine, inasmuch as it does not run direct from one attachment to the other, and that in dissection its position is immediately altered on the division of its connections with the adjoining fascia : bence the student, not having a fixed point of reference, is often at a loss to distinguish between the iliac and femo ral arteries, and mistakes affecting the relations of the most important branches of those vessels are liable to be made. For those reasons it
appears to me that it would be much pre ferable to select some fixed and unchanging point to which to refer the commencement of the artery ; and for this purpose I would suggest the ilio-pectineal eminence of the os innominatum, which, to the student at least, if not to the practical surgeon, will afford an unerring guide to the distinction of the one vessel from the other; the femoral artery, at its entrance into the thigh, being situate im mediately external to the inferior part of that prominence,f with which point the middle of the line connecting the anterior superior spi nous process of the ilium and the symphysis of the pubis will also be found to correspond. The precise situation of the vessel is referred by some to the centre of l'oupart's ligament, or a point midway between the anterior supe rior spinous process of the ilium and the spinous process of the pubes; by others to a point midway between the spinous process of the ilium and the symphysis of the pubes. With regard to this question it is to be ob served that the relation of the artery to the points between which it is situate is not strictly the same in all instances; that in some it witl be found to correspond to the former, and in others to the latter account; but that the latter relation appears to prevail in so much the greater number, that it ought to be adopted as the rule. According to Velpeau it is distant two inches and a quarter from the spinous pro cess of the pubes, and from two and a half to two and three quarters from the superior an terior spinous process of the ilium.
The femoral artery is attended through its entire course by the femoral vein, the two vessels lying in apposition and inclosed within a fihro-cellular investment, to which the ap pellation femoral sheath will be applied. It is also related to the crural nerve or its branches, and it is contained, together with the vein, in a canal of fascia, which will be denominated the _femoral canal.