Internally the artery corresponds, though at a distance, to the pectinalis and adductor mus cles. The femoral vein at the upper part is very nearly upon the same level; the artery, however, is somewhat anterior to it, probably from resting upon the psoas, while the vein corresponds to the pubes between that muscle and the pectinalis: hence the two vessels at their entrance into the thigh, allowance being made for the trifling difference which has been mentioned, lie side by side, the vein internal to the artery; but as the former descends from the pubes, it recedes from the surface more than the artery, and at the same time inclines outward, and thus it becomes posterior to it at the lower part of the stage, so as to be con cealed by the artery by the time it has reached its termination. It is included with the artery in the femoral sheath, and is separated from it by the external of the two septa, which have been described.
In its second stage the relations of the artery differ considerably from those in its first. In the first place it is covered throughout by the sartorius, the muscle crossing it obliquely from without inward, and thence first overlapping it by its inner edge, and gradually extending over it until the vessel is directly covered by it. Secondly, it is in consequence covered by two lamina of the fascia lata enclosing the muscle; one superficial to it, the other beneath it, form ing the front of the femoral canal ; it has then two new coverings, the muscle and the second lamina of the fascia. Thirdly, the femoral vein, which is very closely connected to the artery, is directly behind it, between it and the adduc tor longus muscle, to which the artery corre sponds posteriorly. Fourthly, it has no part deserving of attention upon its inside ; and, lastly, the saphenus nerve is within the femoral canal, along the outer side of the artery and anterior to it.
The inferior third of the artery also presents some peculiarities of relation. The vessel is still covered by the sartorius; but here the muscle is more to the inner, as in the second stage it is more to the outer side of the vessel, not only connecting it in front, but also lying against its inner side, and the more so the nearer we approach the termination of the stage; so much so indeed, that at its termina tion, the artery, when injected, may be felt beneath the outer margin of the muscle; and hence the difference between the mode of pro ceeding with regard to the sartorius recom mended generally to be adopted, when occasion arises for seeking the artery in its inferior third, and that to be pursued when the vessel is to be exposed in its second stage; it being ad vised, in the latter case, to displace the inner edge of the muscle outward, and in the former the outer inward, in order to reach the vessel with the greatest ease and certainty. The ves
sel is also covered by the same two lamina; of the fascia; but the deep one presents at this part remarkable features : it increases in thick ness and is more aponeurotic in proportion as it descends, and hence it is stronger the nearer we approach the termination of the course of the artery ; but in the inferior third its thick ness is still further augmented by numerous tendinous fibres, which pass from the tendons of the adductors longus and magnus to that of the vastus internus, add very much to the thickness of the fascia, and give to it the ap pearance of a tendinous expansion of great strength, connecting the tendons of the mus cles, which have been mentioned, and covering the artery upon its anterior and internal sides. It is also to be observed that this accession of fibres from the tendons exists only in the infe rior third of the artery's course, and not in its middle stage, and hence the covering of the vessel beneath the sartorius, or the anterior wall of the canal, is much thicker and stronger in the former than in the latter ; and hence also one of the difficulties encountered in getting at the vessel in the third stage. The artery in this third stage is situate upon the inside of the shaft of the femur, crossing it ob liquely from before backward : it is not, how ever, in contact with the bone, but is separated from it by the vastus internus muscle : it is enclosed, as before stated, between muscles ; the sartorius before and internal to it, the ad ductors longus and magnus behind it, and the vastus intermis on its outside.
The other relations of the vessel in this stage are to the saphena vein, the saphenus nerve, the femoral vein, and the superficial superior internal articular artery. The first is situate between the femoral artery and the internal face of the thigh, for the most part along the inner margin of the sartorius, but varying some what in this respect, lying at times upon the muscle, from its middle to its inner edge, and at others posterior to it. The saphenus nerve is placed at first, as in the second stage, exter nal and anterior to the artery, but it crosses it at its termination and escapes from the canal, upon its inside, in company with the superficial articular artery, as the vessel is about to pass into the popliteal space. The femoral vein is behind the artery and somewhat external to it : the latter relation of the vein is expressly de nied by Velpeau,* but after careful examina tion the author does not hesitate to affirm it.