rectus

Rectus is a Latin adjective meaning straight or erect. In anatomy, the term rectus is applied to muscles and structures whose fibers or axes run in a relatively straight direction along the body’s long axis. The plural form is recti.

Rectus abdominis: a paired, strap-like muscle running along the front of the abdomen. It originates from the pubic crest and symphysis and inserts into the lower ribs and xiphoid process. Contraction flexes the lumbar spine and increases intra-abdominal pressure. It is innervated by the thoracoabdominal nerves and the subcostal nerve.

Rectus femoris: a member of the quadriceps group in the thigh. It arises from the anterior inferior iliac spine and the ilium above the acetabulum, and inserts on the patella via the quadriceps tendon. It extends the knee and assists hip flexion; innervation is the femoral nerve.

Rectus muscles of the eye: the superior, inferior, medial, and lateral recti. They originate from the common tendinous ring (annulus of Zinn) at the back of the orbit and insert on the sclera. They move the eyeball: the superior and inferior recti elevate and depress, respectively; the medial and lateral recti adduct and abduct. Innervation is cranial nerve III for the medial, superior, and inferior recti, and cranial nerve VI for the lateral rectus.

Rectus capitis muscles: including rectus capitis anterior, rectus capitis lateralis, and the posterior pair, are small suboccipital muscles at the base of the skull. They act to flex or stabilize the head and are innervated by the suboccipital nerve (dorsal ramus of C1).