Internal Abdominal Oblique Muscle
Transversus Abdominus Muscle
Rectus Abdominus Muscle
The External Abdominal Oblique fibers above the level of the ASIS run an inferomedial course from the lower ribs and crest of the ilium. Its aponeurosis above and below the ASIS contributes to the of the rectus sheath. Its aponeurosis continues below the ASIS to the pubic tubercle and crest, and contributes to the formation of several ligaments: inguinal (Poupart's), lacunar (Gimbernat's), pectineal (Cooper's). Its fascia is associated with the superficial inguinal ring, and the outer covering of the spermatic cord.
The Internal Abdominal Oblique fibers above the ASIS run a superomedial course from the inguinal ligament, crest of the ilium, and lower ribs to the posterior layer of the rectus sheath. Its fibers below the level of the ASIS run an inferomedial course. The inferior muscle fibers form the cremaster muscle (middle spermatic fascia). Its aponeurosis continues to the pubic crest and contributes to the anterior and posterior layers of the rectus sheath.
The Transversus Abdominis is associated with the entire costal margin and intercostal spaces 10 and 11. Its fibers above the ASIS run a transverse course and contribute to the posterior layer of the rectus sheath. Its fibers below the ASIS run an inferomedial course to the pubic crest. This represents the major contribution to the Falx Inguinalis.
The segmental Rectus Abdominis arises from the pubic crest and attaches to the costal cartilages of ribs 5,6, and 7. It is interrupted at three transverse levels (xiphoid process, ninth costal cartilage, and umbilicus). These visible features represent the firm attachment of the tendinous inscriptions of the rectus abdominus to the anterior layer of the rectus sheath. The linea alba separates the recti. The Linea Semilunaris marks the lateral margin of the rectus abdominis.
The Rectus Sheath contains the rectus abdominis and pyramidalis muscles, the lower six thoracoabdominal intercostal nerves and their accompanying posterior intercostal vessels, and the superior and inferior epigastric arteries. The rectus sheath is composed of contributions of the aponeuroses of the lateral abdominal wall muscles. The rectus sheath has anterior and posterior layers (laminae). Above the costal margin only the external abdominal oblique and its aponeurosis contribute to the rectus sheath (anterior layer). Between the linea semicircularis, umbilicus, and the costal margin the aponeurosis of the internal oblique splits around the rectus abdominis. In this area the external and internal abdominal oblique aponeuroses form the anterior layer and the internal abdominal oblique and transversus aponeuroses form the posterior layer. Below the linea semicircularis (arcuate) all three aponeuroses pass in front of the rectus abdominis muscle.