The fourth structure, by which the fetnoral artery is covered in the first stage of its course, is the prolongation of the fascia transversalis. The two abdominal fascia, the transversalis and the iliaca, which are, at every other part of the crural arch, either identified and united,, or inserted into bone, are separated in the in terval between the middle of Poupart's and the base of Gimbernat's ligament, and de scend into the thigh, the former in front of or superficial to the femoral vessels, beneath Pou part's ligament and the superficial lamina of the iliac portion of the fascia lata ; the latter behind or deeper than the vessels, between them and the psoas and pectinalis muscles, constituting or continued into the pubic or deep portion of the fascia lata. The two fascia thus leave an aperture beneath Poupart's liga ment, through which the vessels escape from abdomen, and at the same time inclose them between them ; the prolongation of the transversalis covering them in front, the iliac and pubic portion of the fascia lata situate behind them. As it descends upon the vessels, the prolongation from the transversalis is united to the fascia iliaca and iliac portion of the fascia lata upon their outside ; and to the pubic portion upon their inside, in the same manner as the superficial lamina of the iliac portion, and within it in reference to the femoral canal : it may therefore be viewed in one of two lights with regard to that canal, viz. either as de scending into it superficial to the vessels, and entering into the constitution of its anterior wall, or as concurring with the other fascia to form, beneath the superficial lamina of the iliac portion of the fascia lata, a sheath, in which the vessels are immediately contained. The latter is the view which has been adopted by anatomists, and the appellation femoral has been given to the sheath so formed. Like the superficial lamina of the iliac portion of the fascia lata, the prolongation of the fascia trans versalis is wider at Poupart's ligament, and diminishes in width as it descends to the junc tion of the saphena and femoral veins: hence the femoral sheath is considerably larger supe riorly than inferiorly, does not embrace the vessels closely at their entrance into the thigh, and but for the aponeurotic expansion described by Colles, and termed by Cloquet the crural septum, would be open toward the abdomen ; but in proportion as they descend, it invests them more closely until it reaches the entrance of the saphena, at which point its connection to them is Intimate, and from whence the prolon gation seems to the author to be continued down ward into the dense thin cellular or fibro-cellular investment, by which the artery and vein are surrounded and connected together within the femoral canal during the remainder of their course through the thigh. From Sir A. Coo per's account of the prolongation it would appear that it terminated, or cannot be traced further than two inches below Poupart's liga ment. Sir Astley says, " these vessels pass down within the sheath for about two inches, after which they carry with them a closely investing fascia derived from the fascia lata." By the " closely investing fascia," the author understands the proper sheath of the vessels, which has been adverted to, and with which the prolongation of the fascia transversalis appears to him to be identified. According to Professor Harrison,. " it soon becomes thin and indistinct, and is lost in the cribriform part of the fascia lata;" but in this view of its termination the author cannot concur ; the pro longation is doubtless connected to the cribri form fascia (the superficial lamina of the iliac portion of the fascia lata) by the vessels, which traverse both structures, but it is notwith standing separable, without much difficulty, from it, by means of the proceeding already recommended for the display of that part— a proceeding equally applicable to that of the distinct existence and the connections of the expansion in question ; the superficial lamina being at the same time, as directed by Colles, divided from above downward, and its parts held to either side, inasmuch as a thin cellular or adipose stratum is interposed between them. The last particular in the disposition of the prolongation of the fliscia transversalis, having reference to the femoral artery, is, that it is connected to the back of the femoral canal (the pubic portion of the fascia lata posterior to the vessels) by two septa or partitions, placed, one between the artery and vein, upon the inside of the former; the other internal to the latter, between it and the femoral ring: by those the abdominal aperture of the femoral sheath is divided into three compartments: an external one occupied by the artery, a mid dle one by the vein, and an internal by the lymphatics, and at times by a gland. The
two former are so protected that the occurrence of hernia through them is rare; in the case of the first probably impossible; but the internal, whether from weakness or deficiency of pro tecting provisions, allows its protrusion, and hence the relation of the femoral vessels, and more particularly of the artery to the neck of the sac of femoral hernia, upon the outer side of which it is always situate, separated from it by the vein.
At the lower part of the first stage the artery is crossed obliquely by the most internal of the deep branches of the crural nerve, which for distinction sake might be called internal geni eular: it enters the femoral canal on the out side of the vessels above, at a variable distance from Poupart's ligament ; descends from without inward upon the front of the artery within the canal ; and escapes from it below on the inside of the vessel under cover of the sartorius. Situate, as the nerve is, within the femoral canal, upon the front of the artery, and closely connected to it by the femoral sheath, it is very likely, unless care be taken to avoid it, to be included in a ligature at the same time with the vessel : it will not, how ever, be always encountered, inasmuch as it crosses the artery, and at a point higher or lower in different subjects.
At times a second branch of the crural nerve crosses the artery in like manner as the former and lower down, but it is not to be always observed.
Posteriorly in its first stage the artery rests, first upon the inner margin of the psoas magnus, from which it is separated by the deep lamina of the iliac portion of the fascia lata : while so related, it is situate over the anterior surface of the os innominatum, external to the iliopec tioeal eminence, having the two structures, already mentioned, interposed.* Below the os innominatuin it is placed over the head of the femur, from which it is separated by the same parts, and also by the capsular ligament of the articulation, and the synovial bursa, which exists between the front of the capsule, and the psoas and iliacus muscles. There are then in this situation two resisting surfaces against which compression of the vessel may he effected ; and here also, as observed by Harrison, a tumour with pulsation may occur in case of effusion either into the bursa simply, or into the joint, when a communication exists between the former and the synovial membrane of the latter.
having passed the margin of the psoas and the head of the femur, the artery corresponds to the tendon of the psoas and iliacus, to the pectinalis, and to a small portion of the ad ductor brevis, which parts it crosses obliquely in its descent : it is not, however, in contact with them, but is separated from them by a space of some depth occupied by cellular structure and vessels. The distance of the artery from the muscles varies according to circumstances: when the thigh is extended or rotated inward, it is increased; when, on the other hand, it is flexed or rotated outward,* it is diminished : in the former case, the artery is brought nearer to the anterior surface of the thigh by the extension, and by the rotation the lesser trochanter, which is in the middle and deepest part of the space, is carried back ward from that surface.
The vessels which occupy the interval be tween the artery and the muscles are the pro funda vein, the circumflex veins, and the femoral vein in part, they being next to the artery and immediately behind it ; posterior to them are, at times, the profunda artery, and at the upper part, according to circumstances, one or other of the circumflex arteries, when arising, as in ordinary, from it.
External to the artery in its first stage are the psoas and iliacus muscles, the sartorius, the rectus, and the upper extremity of the vastus intemus muscles; from all which it is separated by the wall of the femoral canal. At the entrance of the artery into the thigh, and for about an inch below Poupart's liga ment, the crural portion of the genito-crural nerve is contained within the femoral canal in immediate apposition with the vessel upon its outer side. External to it are situate also the crural nerve above, and itssaphena branch below. Except in rare instances, the profunda artery lies on the outer side of the femoral durinz a greater or less extent of its first stage; but it is, unless occasionally near to its origin, at the same time posterior to it, and is subject to varieties in its relation which will be more particularly detailed in the description of that vessel.