It is necessary to dwell here, for a little, upon the distinction between the two appel lationsfimeral canal and _femoral sheath, that a confusion of the one with the other may not arise. The vessels have in fact, throughout their course, two distinct sheaths, which may be considered peculiar to them, contained the one within the other: the external is formed by the fascia lata in a manlier to be presently explained, and is in all respects analogous to the canal furnished by the cervical fascia to the carotid artery and jugular vein. This outer sheath, which many may regard as the sheath of the vessels, extends from Poupart's liga ment to the aperture by which they escape into the popliteal region, and will, for reasons which will appear more fully by-and-bye, he here called the femoral canal. The second or internal sheath is situate within the former, is of variable thickness, according to the point at which it may be examined, being for the most part very thin; adheres in general closely to the vessels, in which particular it differs from the outer one, within which they are com paratively free ; and not only covers, but also separates them by a thin internal process, which by its density and intimate adhesion to the vessels connects them straitly to each other; it is further not confined, as the other is, to the vessels, while called _femoral, but is prolonged upon them into the popliteal region, where in like manner it invests and connects them : to this investment the denomination femoral sheath will be applied. A distinction between the two structures is necessary in a description of the relations of the femoral artery, were it only to mark their existence, but that which I have adopted is rendered imperative by the use already made of the latter appellation with reference to the anatomy of hernia, in the history of which it is ap plied not to the canal as formed by the fascia lata, but to that, through which the femoral vessels escape from the abdomen, and as formed by the facia' transversalis and iliaca; and the prolongation of the former of these two fasciw being, in my opinion, con tinued into the internal and immediate in vestment of the vessels, it has appeared to me justifiable to extend the signification of the tide femoral sheath, and to apply it to that investment throughout their entire course, as well below as above the saphenic opening of the fascia lata; while his application of the former appellation, femoral canal, is sanc tioned by Cloquet, by whom it is used in the same sense.
Beside those which have been already mentioned, the femoral artery has also, during its course, the following general re lations :—posteriorly it corresponds in suc cession to the psoas magnus, the pectinalis, the adductor brevis, adductor longus and ad ductor magnus muscles; anteriorly it is, in the first part of its course, not covered by any muscle and is comparatively superficial ; and through the remainder and more exten sive portion it is covered by the sartorius. Externally it corresponds to the psoas and iliacus, to the sartorius, the rectus, and lastly to the vastus internus muscles; the latter of which is interposed between it and the inside of the femur : internally it corresponds to the pectinalis and the adductor longus mus cles; and lastly it is overlapped by the sar torius.
It is contained, through its upper half, in the inguinal region. This region is of a triangular prismatic form, the base of the triangle represented by it being above formed by Poupart's ligament, or by a line connecting the anterior superior spinous process of the ilium and the symphysis pubis; its apex below by the meeting of the sartorius and the adductor longus muscles. The sides of the prism are external and internal, inclined, the former backward and inward, the latter backward and outward, and meeting each other along the internal and posterior side of the femur; they are formed, the external by the iliacus and psoas, the rectus, the vastus internus and the sartorius muscles, and the internal by the pectinalis and the adductors.
The base of the prism is in front, consisting of the coverings of the space. During its descent from the os innominatum into the inguinal region, the artery generally inclines inward, describing a curve convex out ward ; and hence, as it seems to me, the entire course of the vessel has been assumed to be inward ; but this first curve, when present, is soon compensated by another in the opposite direction. In its lower half the artery is enclosed between muscles, the vastus internus upon its outside, the adductors longus and magnus behind it, and the sartorius in front.
The course of the femoral artery may be advantageously divided into three parts or stages, to be distinguished as first, second, and third, or as superior, middle, and inferior thirds ; in each of which will be found such peculiarities in the relations of the vessel as will justify the number of subdivisions. They may be defined with sufficient precision by dividing the two superior thirds of the thigh into three equal parts, and they will occupy each, according to the stature, from three to five inches.
The superior stage reaches from Poupart's ligament to the point at which the artery is first covered by the sartorius : during this, its upper third, the vessel is not covered by muscle, except at its termination, where it is overlapped by the inner margin of the sartorius : it is therefore comparatively super ficial, and its pulsations can be felt during life with greater or less facility according to circumstances, to be explained. It has, how ever, four structures interposed between it and the surface, and forming its coverings; viz. the skin, the subcutaneous cellular stratum, the anterior wall of the femoral canal, and the prolongation of the fascia transversalis or the femoral sheath.
The subcutaneous cellular structure pre sents a remarkable difference according to the condition of the subject or certain other cir cumstances. When the body is devoid of fat or emaciated, this structure appears a thin, condensed, dry and lamelliform stratum, con tinued from the abdomen downward upon the lower extremity, and generally denominated the superficial fascia of the thigh; but when, on the contrary, the body is in good condition, and the quantity of superficial adeps is con siderable, the appearance of a membranous expansion is removed, and in its stead a thick and uniform stratum of fat is found in terposed between the skin and the fascia lata. In other cases presenting a medium condition, the stratum of fat and the membranous expan sion may be both observed : in such case the former is generally superficial, and the latter underneath ; but when the accumulation of adeps in the subcutaneous structure is more considerable, e.g. in the healthy infant or in many adults, particularly among females, no trace of superficial fascia is to be found. So much for the varieties which the subcutaneous cellular structure presents naturally. It is also found frequently in abnormal conditions deserving of attention : at times it is divisible to a greater or less extent into a succession of expansions, having each the appearances of fasciae and being of indeterminate number : this disposition, which occurs not unfrequently, and is of considerable importance in a practical point of view, appears due to the influence of pressure exerted by tumours, e.g. that of hernia. Again, in anasarca the subcutaneous structure becomes greatly increased in depth, and loses all appearance of membrane, seeming then a deep gelatinous stratum, consisting of the cellular structure and the effused serum.