PSOAS MAJOR:
The Psoas Major muscle is a fusiform muscle of approximately 16 inches in the adult and is the largest, thickest muscle, termed the tenderloin in beef.
It has a superficial and deep layer; the former arises from the transverse processes of L3-5 and the brim of the lesser pelvis. The superficial layer arises from the lateral surface of the lower thoracic and all lumbar vertebrae plus their associated discs. These two muscle layers traverse downward and laterally under the inguinal ligament and over the iliac fossa to become continuous with the iIiacus muscle. In humans, the psoas is a combination of fast and slow twitch fibres. The lumbar plexus passes between the two layers of psoas major.
PSOAS MINOR:
This exists in only 50% of humans. It is a long slender skeletal muscle running anterior to the medial border of psoas major and is a weak flexor of the hip. Psoas minor arises from the facets of T12-L1 and inserts into the iliopectineal eminence. Fibres also stretch and attach to the deep iliac fossa with fibres to the inguinal ligament.
ILIACUS:
This flat wide muscle fans from the borders of the iliac fossa downward to blend with fibres of the psoas muscle(s) before attaching to the lesser trochanter.
Jen Guest
Secretary, Physiotherapist, Pilates Practitioner
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