Internal Abdominal Oblique Muscle

The internal abdominal oblique (Figs. 1.9,1.10) muscle is much thinner and lies deep to the external abdominal oblique. It arises from the iliac crest and the lateral two-thirds of the inguinal ligament, as well as from the tho-racolumbar fascia. Fibers of this muscle, particularly those from the iliac crest and thoracolumbar fascia, pursue a reverse course perpendicular to that of the external abdominal oblique, extending for the most part upward and medially.

The part of the muscle that originates from the inguinal ligament becomes aponeurotic and arches over the spermatic cord in the male, or the round ligament in the female. It joins the aponeurosis of the transverse abdominis muscle anterior to the rectus abdominis muscle to form the conjoint tendon (falx inguinalis). It attaches to the pubic crest and for a variable distance to the medial part of the pecten pubis. In the Bassini technique of herniorrhaphy [24-26], the conjoint tendon is sutured to the transversalis fascia and the reflected part of the inguinal ligament. The conjoint tendon joins medially the anterior wall of the rectus sheath and unites laterally with the interfoveolar ligament, an inconstant fibrous

Deltoid Muscle

Internal Oblique Abdominis

Fig. 1.9. Direction of the fibers of the external and internal abdominal oblique muscle

Deltoid Muscle

Internal Oblique Abdominis

Fig. 1.9. Direction of the fibers of the external and internal abdominal oblique muscle

Symphysis Pubis

Pubic Tubercle

Pectoralis Major

Cut Margin of the External Oblique Abdominis Aponeurosis

External Oblique Abdominis Rectus Abdominis

Rectus Sheath Pubic Tubercle

Symphysis Pubis

Pectoralis Major

Cut Margin of the External Oblique Abdominis Aponeurosis

External Oblique Abdominis Rectus Abdominis

Rectus Sheath Pubic Tubercle

Serratus Anterior Muscle

Internal intercostal Muscle

External Intercostal Muscle

Internal Abdominal Oblique

Fig. 1.10. Fibers of the internal abdominal oblique muscle and aponeurosis in relationship to the rectus abdominis muscle

Internal intercostal Muscle

External Intercostal Muscle

Internal Abdominal Oblique

Internal Abdominal Oblique Muscle

Camper's Fascia

Skin

Rectus Abdominis

Camper's Fascia

Skin

Rectus Abdominis band that connects the transverse abdominis to the superior pubic ramus. However, variations do exist in regard to the extent of attachment of the conjoint tendon and its structural characteristics. The part of the tendon that inserts on the pecten pubis extends posterior to the superficial inguinal ring, forming a natural barrier that prevents the occurrence of inguinal hernia. A direct inguinal hernial pouch may pass through this tendon, acquiring the coverings of this structure.

The posterior fibers of the internal abdominal oblique muscles that gain origin from the iliac crest extend upward and laterally to the inferior border of the lower three or four ribs, continuing with the internal intercostal muscles. They become aponeurotic towards the midline and contribute to the formation of the linea alba by joining the aponeurosis of the flat abdominal muscles of the same and opposite side.

Superior to the midpoint between the umbilicus and the symphysis pubis (upper two-thirds), the internal oblique aponeurosis divides into two layers. The anterior layer covers the anterior surface of the rectus abdomi-nis and the posterior layer invests the posterior surface of the rectus abdominis. Distal to this site (lower one-third), the aponeurosis of the internal oblique remains a single layer anterior to the rectus abdominis (Fig. 1.11).

The loosely arranged fasciculi of the internal oblique muscle and its aponeurosis, which extend around the spermatic cord and testis, constitute the cremasteric muscle and fascia that invariably receive fibers from the transverse abdominis. The cremasteric, a striated muscle with a lateral and a medial part, is an involuntary muscle innervated by the genital branch of the genitofemoral nerve (L1, L2). The lateral part is thicker, directly arises from the inguinal ligament, and extends to the anterior superior iliac spine. The medial part of the internal abdominal oblique, which is sometimes absent, arises from the pubic tubercle, conjoint tendon, and possibly the transverse abdominis.

From the inferior edge of the internal abdominal oblique, the cremasteric muscle and fascia loop over the spermatic cord and testis to terminate at the pubic tubercle and merge with the anterior layer of the rectus sheath. This muscle is considered to have internal and external components separated by the internal spermatic fascia [27]. Redman [28] concluded that exposure of the inguinal canal and deep inguinal ring in her-nial repair is greatly enhanced by careful dissection of the cremasteric muscle and fascia.

In the female, the round ligament is invested by the sporadic fibers from the lateral part of the cremasteric muscle. Contraction of the cremasteric muscle mediates the cremasteric reflex, a brisk reflex, particularly in children, which involves elevation of the testicles towards the superficial inguinal ring upon stimulation of the inner thigh.

Rectus Abdominis

External Abdominal Oblique Muscle

Rectus Abdominis

External Abdominal Oblique Muscle

External Abdominal Oblique Muscle

Oblique Aponeurosis Costal cartilage

Transverse Abdominis Muscle & Aponeurosis

External Abdominal

Camper's Fascia Rectus Abdominis

Anterior Layer of the Rectus Sheath

Oblique Aponeurosis Costal cartilage

External Abdominal Oblique Muscle

Camper's Fascia Rectus Abdominis

Anterior Layer of the Rectus Sheath

External Abdominal Oblique Muscle

Investing Layer Deep Cervical Fascia

Internal Abdominal Oblique

External Abdominal Oblique Muscle

Transverse, Abdominis Muscle

Internal Abdominal Oblique

External Abdominal Oblique Muscle

Transverse, Abdominis Muscle

Fig. 1.11. Patterns of lamination of the rectus sheath

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  • Delfina
    Are internal abdominal oblique muscles superficial or deep?
    8 years ago

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