What do the names of the external and internal oblique muscles, mean?
The name internal obliques refers to the location and shape of the muscle.
Internal means inside.
Oblique comes from the Latin word obliquus which means a slanting orientation.
The slanting direction refers to the direction of the fibers of this muscle. The fiber direction of the internal obliques is in the direction of reaching across your body. As in, if you place your hand on the opposite side of your abdomen, your fingers represent the direction of the fibers.
The name external obliques also refers to the location and shape of the muscle.
External means outside.
Oblique, as we just said, means a slanting orientation and refers to the muscle fiber direction.
The fiber direction of these muscles is like the direction of reaching into your pockets.
Where do the external and internal oblique muscles attach?
The internal obliques originate on the inguinal ligament (a ligament that runs from the anterior iliac spine to the pubic bone) and the anterior iliac crest.
The external obliques originate on the lower 8 ribs.
The internal obliques insert onto the costal cartilages of the lower 4 ribs, the abdominal aponeurosis (a superficial sheet of connective tissue over the abdomen), and the linea alba. (The linea alba is a fibrous band of connective tissue that runs from the xiphoid process to the pubic symphysis.)
The external obliques insert onto the abdominal aponeurosis, the linea alba, the iliac crest, and the pubic bone.
What actions do the external and internal oblique muscles do?
In the case of these abdominal muscles, stabilization is a key function.
The internal obliques function bilaterally (both sides) to flex the trunk and compress its contents. They function unilaterally (one-sided) to laterally flex the trunk and rotate it to the same side.
The external obliques function bilaterally to flex the trunk and compress its contents.
They function unilaterally to laterally flex the trunk and rotate the trunk to the opposite side.