Anatomy in detail:
The rectus femoris muscles lie over the anterior (front) of the femur, extending from pelvis to tibia, spanning the hip and knee joints.
rectus ≅ straight
femoris ≅ femur
When fully engaged, the rectus femoris muscles correctly position the legs to the torso.
The rectus femoris is part of the quadriceps femoris muscle group, along with the 3 "vasti" muscles: the vastus lateralis, vastus intermedius and vastus medialis.
The rectus femoris is the only muscle of the quadriceps that attaches to the pelvis. The three vasti attach to the top of the femur.
Distally, the four muscles of the quadriceps femoris merge into the common tendon of the quadriceps.
The rectus femoris can be thought of as the lead muscle of the quadriceps, crossing both hip and knee thus aligning these joints.
The common tendon of the quadriceps attaches to the patella, the largest sesamoid bone (a bone embedded in connective tissue) in the human body.
From the patella, the connective tissue continues as the patellar ligament.
The patellar ligament attaches to the tibial tuberosity located on the proximal, anterior aspect of the tibia. The tibial tuberosity is the distal attachment of the rectus femoris.
The proximal attachments of the rectus femoris to the pelvis are commonly described as "to the ilium of the pelvis via two heads - the straight head and the reflected head". But it is not that simple. Variations in the pelvic attachments have been observed.
The heads of the rectus femoris merge into an aponeurosis which continues distally on the anterior surface of the muscle.
The lower two-thirds of the posterior surface of the rectus femoris consists of a thick, broad aponeurosis that becomes the superficial, central part of the common quadriceps tendon.
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