Internal abdominal oblique muscle

The internal oblique muscle of the abdomen is a flat, leaf-shaped muscle located deep to the external oblique muscle of the abdomen and superficial to the transverse muscle of the abdomen. It originates at the thoracolumbar fascia and the greater trochanter, and its fibers generally extend in a cranioventral direction, perpendicular to those of the external oblique muscle.

Insertion/Origin: The internal oblique muscle of the abdomen has a fleshy part that originates on the dorsolateral third of the inguinal arch, on the ventro-cranial iliac spine and iliac crest, and on the edge of the thoracolumbar fascia. Its aponeurosis ends on the inner surface of the last three or four costal cartilages and along the entire linea alba, up to the prepubic tendon, where it joins the aponeurosis of the external oblique muscle.

Relationships: The internal oblique muscle of the abdomen is completely covered by the external oblique muscle. At the inguinal fold, it attaches to the inguinal arch and then detaches ventrally, delimiting the inguinal canal with it. At this level, part of the internal oblique gives rise to the cremaster muscle, which is considered to be dependent on this muscle. The internal oblique muscle covers the rectus and transverse muscles of the abdomen, and its aponeurosis participates in the formation of the sheath of the rectus muscle of the abdomen.

Action: Together with the other abdominal muscles, it compresses the abdominal viscera. This action, called abdominal press, is involved in vital functions such as exhalation. The muscle indirectly contributes to the flexion of the spine.

Blood supply: By the dorsal intercostal, lumbar, and circumflex iliac arteries and, in certain species such as carnivores, pigs, and rabbits, by the cranial abdominal arteries and branches of the musculophrenic, cranial epigastric, and caudal arteries.

Nerve: By the intercostal nerves of the spaces covered by the insertions of the fleshy part and by the ventral branches of the first two or three lumbar nerves.