The iliacus is a flat, triangular muscle which fills the

iliac fossa The iliac fossa is a large, smooth, concave surface on the internal surface of the Ilium (bone), ilium (part of the three fused bones making the hip bone). Structure The iliac fossa is bounded above by the iliac crest, and below by the Arcuate ...

. It forms the

lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

portion of

iliopsoas The iliopsoas muscle (; ) refers to the joined psoas major and the iliacus muscles. The two muscles are separate in the abdomen, but usually merge in the thigh. They are usually given the common name ''iliopsoas''. The iliopsoas muscle joins t ...

, providing

flexion Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

of the

thigh In anatomy, the thigh is the area between the hip (pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of bone tissu ...

and

lower limb Lower may refer to: *Lower (album), ''Lower'' (album), 2025 album by Benjamin Booker *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Gloucestershire, England See also

*Nizhny {{Disambiguation ...

at the acetabulofemoral joint.

Structure

The iliacus arises from the

on the interior side of the

hip bone The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the Ilium (bone) ...

, and also from the region of the

anterior inferior iliac spine The anterior inferior iliac spine (AIIS) is a bony eminence on the anterior border of the hip bone, or, more precisely, the wing of the ilium. Structure The AIIS is a bony eminence on the anterior border of the ilium. It is below the anterior ...

(AIIS). It joins the

psoas major The psoas major ( or ; from ) is a long fusiform muscle located in the lateral lumbar region between the vertebral column and the brim of the lesser pelvis. It joins the iliacus muscle to form the iliopsoas. In other animals, this muscle is e ...

to form the

. It proceeds across the iliopubic eminence through the muscular lacuna to its insertion on the

lesser trochanter In human anatomy, the lesser trochanter is a conical, posteromedial, bony projection from the shaft of the femur. It serves as the principal insertion site of the iliopsoas muscle. Structure The lesser trochanter is a conical posteromedial p ...

of the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

. Its fibers are often inserted in front of those of the psoas major and extend distally over the

.Platzer (2004), p 234

Nerve supply

The iliopsoas is innervated by the

femoral nerve The femoral nerve is a nerve in the thigh that supplies skin on the upper thigh and inner leg, and the muscles that extend the knee. It is the largest branch of the lumbar plexus. Structure The femoral nerve is the major nerve supplying the ant ...

and direct branches from the

lumbar plexus The lumbar plexus is a web of nerves (a nerve plexus) in the lumbar region of the body which forms part of the larger lumbosacral plexus. It is formed by the divisions of the first four lumbar nerves (L1–L4) and from contributions of the su ...

.''Thieme Atlas of Anatomy'' (2006), p 422

Function

In open-chain exercises, as part of the

, the iliacus is important for lifting (flexing) the femur forward (e.g. front scale). In closed-chain exercises, the iliopsoas bends the trunk forward and can lift the trunk from a lying posture (e.g. sit-ups, back scale) because the psoas major crosses several vertebral joints and the

sacroiliac joint The sacroiliac joint or SI joint (SIJ) is the joint between the sacrum and the ilium bones of the pelvis, which are connected by strong ligaments. In humans, the sacrum supports the spine and is supported in turn by an ilium on each side. The ...

. From its origin in the lesser pelvis the iliacus acts exclusively on the

hip joint In vertebrate anatomy, the hip, or coxaLatin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) (: ''coxae'') in medical terminology, refers to either an anatomical region or a joint o ...

Additional images

File:Iliacus muscle - animation05.gif, Position of iliacus muscle (shown in red). Animation. File:Gray236.png, Right

. Internal surface. Iliac fossa visible at upper left.

Notes

References

* *

External links

PTCentral
* - "Muscles and nerves of the posterior abdominal wall." * (, ) {{Authority control Hip flexors Hip muscles Iliopsoas muscles Muscles of the lower limb