Q. Which of the following muscles is NOT a boundary of the retroperitoneum?
The psoas muscle
The iliacus muscle
The quadratus lumborum muscle
The diaphragm
The rectus muscle
The posterior surface of the retroperitoneum is formed by the lumbar vertebral bodies in the midline, which are covered by the shiny, longitudinal fibers of the anterior spinous ligament. These are flanked bilaterally by the psoas muscles. The psoas muscles are covered by a glistening white fibrous fascia, the so-called psoas sheath, which is contiguous with the transversalis fascia. As one moves laterally, the lateral portion of the quadratus lumborum extends from behind the lateral margin of the psoas.
The anterior layer of the lumbodorsal fascia covers this muscle and continues as the aponeurosis of the transversus abdominis muscle.
Farther laterally, the transversus abdominis muscle proper is encountered. Superiorly, the posterior wall of the retroperitoneum is formed by the posterior insertion of the diaphragm along the lower ribs. Inferiorly, below the level of the iliac crest, the iliopsoas muscle forms the posterior confine of the retroperitoneum.