The external oblique aponeurosis

The aponeurosis of the external oblique muscle fuses with the aponeurosis of the internal oblique in the anterior rectus sheath. This line of fusion is considerably medial to the semilunar line - the fusion line is oblique and somewhat semilunar, being more lateral above and more medial below. In fact, the external oblique aponeurosis contributes very little to the lower portion of the anterior rectus sheath. This latter point is of considerable importance in inguinal hernioplasty (Fig. 14.5).

There is a defect in the external - oblique aponeurosis just above the pubis. This aperture - the superficial inguinal ring -is triangular in shape and in the male allows passage of the spermatic cord from the abdomen to the scrotum. In the female the round ligament of the uterus passes through this opening. The superficial inguinal ring is not a 'ring'; it is a triangular cleft with its long axis oblique in the same direction but not quite parallel to the inguinal ligament. The base of the triangle is formed by the crest of the pubis and the apex is lateral towards the anterior superior iliac spine. The superficial inguinal ring represents that interval between the aponeurosis of the external oblique which inserts into the pubic bone superiorly and, as the inguinal ligament, inserts into the pubic tubercle inferiorly. The aponeurotic margins of the ring are described as the superior and inferior crura. The spermatic

Figure 14.5. The external oblique muscle and its aponeurosis invests the abdomen.

cord, as it comes through the superficial ring, rests on the inferior crus which is a continuation of the floor of the inguinal canal (the upturned internal margin of the inguinal ligament).

The crura of the superficial ring are joined together by intercrural fibres derived from the outer investing fascia of the external oblique aponeurosis. The size and strength of these intercrural fibres vary.

The external oblique aponeurosis in the region of the groin forms a free border known as or the inguinal ligament, which is simply the lower margin of this aponeurosis; it is not a condensed thickened ligamentous structure. The ligament presents a rounded surface towards the thigh where the aponeurosis is rolled inwards back on itself to make a groove on its deep surface. Laterally the ligament is attached to the anterior superior iliac spine and medially to the pubic tubercle and via the lacunar and reflected inguinal ligaments to the iliopectineal line on the superior ramus of the pubis. The inguinal ligament is not straight; it is concave, with the concavity directed medially and upward towards the abdomen.

The medial attachment, or continuation, of the inguinal ligament as the lacunar (Gimbernat's) and the pectineal (Cooper's) ligament gives a fan-like expansion of the inguinal ligament at its medial end, which curves posteriorly to the iliopectineal ligament. This expansion has important surgical implications.

The lacunar ligament is a triangular continuation of the medial end of the inguinal ligament. Its apex is at the pubic tubercle, its superior margin continuous with the inguinal ligament and its medial margin is attached to the iliopectineal

External oblique

Iliopectineal line (Cooper's ligament)

Reflected part of inguinal ligament Femoral artery and vein

Lacunar ligament Pubic tubercle

External oblique

Figure 14.6. The upper abdominal surface of the attachment of the inguinal ligament to the pubic tubercle is the floor of the inguinal canal.

line on the superior ramus of the pubis. Its lateral crescentic edge is free and directed laterally, where it is an important rigid structure in the medial margin of the femoral canal. The ligament lies in an oblique plane, with its upper (abdominal) surface facing superomedially and being crossed by the spermatic cord, and its lower (femoral) surface looking anterolater-ally. With the external oblique aponeurosis and the inguinal ligament, the superior surface forms a groove for the cord as it emerges from the inguinal canal (Fig. 14.6).

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