The structures of the second order of parts concerned with our subject, are the aponeurosis of the external oblique muscle, the internal oblique and the transversalis muscles; of these the first, which is immediately beneath the fascia, extends over the entire anterior wall of the fossa reaching from the linen semilemaris above to the crural arch below ; internally it is united with that of the other side in the linen alba, and inferiorly it forms the crural arch by its border, which is attached externally to the superior anterior spinous process of the ilium, internally to the spinous process of the pubis, and in the interior to the iliac fascia and the fascia lata. The direction of this band is to be borne in mind, for it does not run directly from one of these points of bone to the other ; but it descends toward the thigh, and recedes from the surface at the same time that it passes in ward, hence it is concave both forward toward the surface and upward toward the abdomen ; the cause of this direction is its connection inferiorly and posteriorly with the fascia lata and the fascia iliaca. The aponeurosis consists primanly of tendinous fibres which run in the same direction as the fibres of the muscle, i. e., downward and inward, parallel to each other, and also to the crural arch, though rather con verging toward it internally, and thereby form a tendinous expansion ; the longitudinal fibres of the aponeurosis are crossed by others which run downward and outward ; these are very irregular in number and do not interlace with the former, to which they are superficial ; hence the aponeurosis does not possess great strength in the transverse direction, and its longitudinal fibres are liable to be separated, and deficien cies to be thereby formed in the aponeurosis, which are riot unfrequently to be observed. The superficial inguinal ring is seated in the aponeurosis ; this aperture, for the particulars of which see the articles ABDOMEN and IlEaNtA, is of variable form and size ; in some cases it is elliptical, in others triangular ; in the male it is larger than in the female ; its position is oblique, the longer diameter inclining from the pubis upward and outward toward the superior anterior spinous process of the ilium ; its actual length is extremely variable, in sonic instances nut amounting to half an inch, in others exceeding an inch.
The inferior part of the internal oblique and of the transversalis muscles, which alone is concerned in the anatomy of this part of the abdominal wall, may be distinguished into two parts, viz., their muscular portion and their aponeurosis. The muscles are both, but more particularly the latter, very thin, though of great width; they are placed the one within the other, and the internal oblique, which is super ficial to the transversalis, also descends a good deal lower, so that its inferior margin approaches very close to the crural arch, leaving only suf ficient space between them for the escape of the spermatic process, which it covers beneath the aponeurosis of the external oblique, and which in some instances passes between its fibres,* while the margin of the transversalis is at some distance from the arch, and rarely covers the process, at least to any extent, the process escaping from the deep ring, for the most part below the margin of the muscle ; Cloquet has even seen the margin of the muscle so far as two fingers' breadth above the point of escape of the cord, and its fibres are usually pale, fine, and scattered. The muscular fibres of the lower part of the two muscles are at tached to the anterior extremity of the crest of the ilium and to its spinous process, also to the superior aspect of the outer part of the crural arch, the oblique to nearly the outer half of the arch, the transverse to the outer third or fourth, but the ultimate attachment of the latter is to the surface of the fascia iliaca above the arch, to which they adhere very intimately as they pass forward from the fascia ; they run inward nearly transversely, but convex forward in proportion to the prominence of the abdo men, those of the oblique over the deep ring, and the spermatic process within the inguinal canal, those of the transverse above the ring, until they have both passed that point ; they then descend along the inside of the process, and at the same time recede from the surface so that they become posterior to it, and terminate as they descend in a thin irregular aponeurotic expansion common to the fibres of both mus cles, and thence denominated " the conjoined tendon ;" though designated by an especial name, this is in reality only the inferior part of the general conjoined tendon of the two mus cles which terminate between the umbilicus and the pubis in a common expansion ; this is placed superficial to the rectus muscle, and is inserted into the lines alba, the anterior margin of the crest of the pubis as far as its spinous process, and thence outward into the pectineal line of the bone, there forming the " conjoined tendon" of the anatomy of hernia. This struc
ture is situate behind the spermatic process, between it and the fascia transversalis; it ap proaches very near to the inner margin of the deep ring, and at its insertion into the pectineal line it meets and is identified with Gimbernat's ligament; it is closely adherent to the surface of the fascia transversal's, and hence that fascia presents an appearance of thickness and strength upon the inside of the deep ring, which it does not really possess. From the inferior margin of the internal oblique and from the superior side of the crural arch the cremaster muscle descends upon the anterior and external part of the spermatic process, forming one of the coverings of the process within the inguinal canal, of course concealing it after the division of the aponeurosis of the external oblique, and requiring to be detached from the arch along with the lower fibres of the internal oblique in order that the process may be fairly exposed.
The deep structincs of the anterior wall of the iliac fossa are also three, viz., the fascia transversal's, the fascia propria, and the peri toneum.
1. The fascia transversalis is most remark able in the iliac region, but it is not con fined to it, being to be traced upward to the surface of the diaphragm, and backward round the interior of the lateral walls of the abdo men. In the iliac region this fascia is inferiorly first identified with the fascia iliaca from a short distance behind the anterior superior spinous process of the ilium to the outer side of the external iliac artery, or about the middle of the crural arch ; the line of its connection with the fascia iliaca runs downward, forward, and in ward, at a short distance within the crest of the ilium and the crural arch, approaching the latter, however, as it descends, until at the outside of the artery it touches it; it is sepa rated along this line into two laminae which enclose the circumflex iliac artery between them; there is, therefore, an interval between the arch and the line of connection of the two fasciae in which the fascia iliaca intervenes, and to the surface of this part of the fascia it is that the internal oblique and transverse muscles are attached. In the second place the fascia transversalis descends into the thigh beneath the crural arch, between it and the iliac vessels, and forming the front of their sheath; and, thirdly, it is attached upon the inside of the vessels, along the pectmeal line of the pubis posterior to the conjoined tendon of the internal oblique and transverse muscles, between it and the peritoneum, and separated by it from the spermatic process, which is in front of both.