Morphology of Psoas Minor and Psoas Accessorius

Psoas minor muscle is considered to be a vestigial muscle like palmaris longus and plantaris. It lies anterior to the psoas major muscle. It has a small fleshy belly and a long flat tendon. This small muscle is the representative in man of a relatively large muscle which in most mammals plays an important part of flexing the lumbar part of vertebral column. In some lower mammals it is larger than psoas major and acts as a flexor of pelvis; this being utilized in running by the rabbit and the apes in brachiating. It begins to disappear in those primates which assume the erect posture. The presence of this muscle varies from person to person and on the two sides. It is present in about 40 to 60% of the population. In the majority it is inserted on the iliopubic eminence but may also be attached to the arcuate line of ilium and the iliac fascia. While going through the literature we did not come across any detailed study of the muscle in the population of this region. Hence, we have conducted a detailed study of psoas minor muscle in 30 cadavers bilaterally. In the present series this muscle was absent in 70%. Average length of fleshy belly was 8.23 cm and that of the tendon 15.48 cm. In some cases an unusual interesting feature observed was the origin of some fibers of psoas major from the deep surface of flattened tendon of Psoas minor muscle, which we have named as Psoas accessorius.