Three flat muscles of the anterior abdominal wall—
the external oblique, internal oblique, and transversus abdominis—lie in three layers [Figs.
8.3, 8.6]. Each muscle is muscular posterolaterally and aponeurotic anteromedially. Two other mus-cles, the rectus abdominis and pyramidalis are located close to the midline. As the aponeuro-ses of the three flat muscles approach the midline, they partially enclose the rectus abdominis muscle between them to form the rectus sheath. Medial to the rectus abdominis, the three aponeuroses fuse with each other and with the aponeuroses of the opposite side in the median raphe—the linea alba. The linea alba extends from the xiphoid pro-cess to the pubic symphysis.
The outer two muscles—the external and inter-nal obliques—are approximately fan-shaped. The external oblique takes origin superiorly from the external surfaces of the lower eight ribs and radiates downwards and forwards. It has a long linear inser-tion into the linea alba, pubic crest, pubic tubercle, and the anterior two-thirds of the iliac crest. (Fibres of the external oblique reach the linea alba by pass-ing in front of the rectus abdominis. As such they DISSECTION 8.3 Cutaneous nerves of
the anterior abdominal wall Objective
I. To find the anterior and lateral cutaneous branches of the abdominal nerves.
Instructions
1. Divide the superficial fascia vertically in the median plane, and in the line of the posterior axil-lary fold as far as the iliac crest.
2. Reflect the fascia by blunt dissection between these two cuts. Find the anterior and lateral cuta-neous branches of the intercostal nerves as they emerge from the anterior and lateral parts of the abdominal wall.
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Muscles of the anterior abdominal wall
contribute to the anterior wall of the rectus sheath).
Between the pubic crest and anterior superior il-iac spine, the free margin of the external oblique aponeurosis forms the inguinal ligament [Fig. 8.3].
At the pubic tubercle, the deep fibres of the inguinal ligament curve horizontally backwards to the me-dial part of the pecten pubis as the lacunar liga-ment. Other fibres continue along the pecten pubis to the iliopubic eminence as the pectineal liga-ment [Fig. 8.7]. Over the lateral half of the pubic crest, there is a triangular deficiency in the aponeu-rosis of external oblique—the superficial ingui-nal ring. The medial and lateral margins of the su-perficial inguinal ring are also known as the medial and lateral crus. The spermatic cord in the male and the round ligament of the uterus in the female pass through the superficial inguinal ring [Fig. 8.2].
The internal oblique takes origin inferiorly from the thoracolumbar fascia, the iliac crest, and the lateral two-thirds of the inguinal ligament
[Fig. 8.7]. It radiates upwards and forwards and is inserted into the costal margin, the linea alba, and the pubic crest [Fig. 8.3]. The lower fibres of the internal oblique fuse with similar fibres of the transversus abdominis to form the conjoint tendon. The conjoint tendon turns downwards and is inserted into the pubic crest and the pecten pubis [Figs. 8.6, 8.8]. (Fibres of the internal oblique which are inserted into linea alba have different relations to the rectus abdominis in different re-gions. In the upper three-fourths the aponeurosis splits into two. The anterior part goes in front of the rectus and fuses with the aponeurosis of exter-nal oblique. This part contributes to the formation of the anterior wall of the rectus sheath. The poste-rior part goes behind the rectus and fuses with the aponeurosis of transversus abdominis. This part contributes to the formation of the posterior wall of the rectus sheath. In the lower one-fourth of the abdomen, the internal oblique aponeurosis passes
Posterior wall of rectus sheath
Superior epigastric A.
Intercostal N.
Transversus abdominis
Inferior epigastric A.
Arcuate line of rectus sheath
Internal oblique
Transversalis fascia
Rectus abdominis Inguinal canal Rectus abdominis
Lateral edge of rectus sheath External oblique
Internal oblique Cut edge of external oblique IIiohypogastric N.
Cremaster M.
Reflected ligament
Spermatic cord Conjoint tendon
Fundiform ligament of penis
Fig. 8.6 Deep dissection of the anterior abdominal wall. On the left side of the body, the external and internal oblique muscles, the anterior wall of the rectus sheath, and the greater part of the rectus abdominis have been removed. On the right side the external oblique and upper parts of the internal oblique and the upper part of the anterior wall of the rectus sheath have been removed.
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The anterior abdominal wall
in front of the rectus abdominis, contributing only to the anterior wall.)
The posterior fibres of the external oblique and the posterior fibres of the internal oblique are al-most vertical and unite the iliac crest and the rib cage. The upper fibres of the external oblique and the lower fibres of the internal oblique are nearly horizontal. The middle fibres of both cross each other at right angles. From the lower margin of the internal oblique, muscle fibres pass over the spermatic cord to form the cremaster muscle
[Fig. 8.8]. The cremaster loops down around the spermatic cord and turns upwards to be attached to the pubic tubercle.
The innermost muscle—the transversus ab-dominis—is horizontally placed [Fig. 8.6]. It takes origin from the internal surface of the rib cage, the thoracolumbar fascia, the iliac crest, and the lateral one-third of the inguinal ligament. It runs forward to be inserted into the linea alba. (In the upper two-thirds of the abdominal wall, the muscle fibres pass behind the rectus abdominis, and contribute to
External
oblique Anterior superior
iliac spine Inguinal ligamentPectineal ligament Lacunar ligament
Obturator foramen
Internal oblique Transversus abdominis
Latissimus dorsi Quadratus lumborum
lliolumbar ligament
Posterior superior iliac spine
Fig. 8.7 The bony pelvis and fifth lumbar vertebra seen from above.
Aponeurosis of internal oblique
Internal oblique
Inguinal ligament External oblique (reflected)
Cremaster M. on spermatic cord
Membranous layer of superficial fascia Conjoint tendon
Reflected ligament
Suspensory ligament of penis
External spermatic fascia
Fig. 8.8 Inguinal region. The external oblique is turned down to show the spermatic cord in the inguinal canal.
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Muscles of the anterior abdominal wall
the posterior wall of the rectus sheath. In the lower one-third the fibres of transversus abdominis pass in front of the rectus abdominis and contribute to the anterior wall of the rectus sheath.) The muscle fibres of the transversus abdominis lie at an angle to the intermediate fibres of both the external and inter-nal obliques but are parallel to those of the exterinter-nal oblique superiorly and to the internal oblique infe-riorly. This arrangement gives maximum strength to the abdominal wall and holds the abdominal con-tents in place when the intra-abdominal pressure is raised by contraction of these muscles.
Nerve supply: these muscles are supplied by the ventral rami of the lower five or six intercostal nerves and the subcostal nerve. In addition, the in-ternal oblique and transversus abdominis are sup-plied by the iliohypogastric nerve. The cremaster muscle is supplied by the genital branch of the genitofemoral nerve.