Front View i. bones:
1 Pubis: of the pelvis
2 Femur: thigh bone
3 The head of the femur
4 The neck of the femur
5 The great trochanter
1 The rectus femoris: arises by two tendons from the pelvis to join the common tendon of the triceps femoris a short distance above the knee.
2 The adductor muscles, longus and magnus: arise from the pubic and ischium portions of the pelvis to be inserted into the whole length of the femur on its inner side.
3 Vastus externus: from the femur at the great trochanter; following a rough line at the back of the shaft to join the common tendon a little above the knee.
4 The vastus internus: arises from the front and inner side of the femur to nearly the whole length of the shaft to be inserted into the side of the patella and common tendon.
The triceps of the thigh comprise the rectus, vastus externus and internus, adding the crureus, a deep seated muscle, which makes four in all. These four are together called the quadriceps extensor. They all meet above and around the knee to a common tendon that is inserted into the patella and continued by a ligament to the tubercle of the tibia.
The rectus is seen above as it emerges from between the tensor vaginae femoris and the sartorius. From here it descends vertically on the surface of the thigh to join to its tendon above the knee. The rectus muscle bulges out at a much higher level than the muscles on either side. The outer muscle ends as a triangular tendon to enter the patella above the knee. The inner is placed quite low on the thigh and seen distinctly at its lower margin. It passes round the inner side of the knee to its insertion into the patella.
The human body is provided with a system of levers and pulleys by which muscles pull on the movable bones. The thigh swings backward as well as forward. When in action, all the muscles that surround the hip joint are geared and set in motion. The triceps of the thigh like the triceps of the arm is composed of three muscles that act together. When they pull they extend the leg on the thigh.
The thigh bone is the most perfect of all levers, it is balanced by the muscles that pass up from the "crank shaft" of the thigh bone to the pelvis. These muscles work against one another in turning the round slippery head of the thigh bone in the socket. The muscles parallel the shaft to control the action of the knee joint. The extensors of the leg are in front or on top when the thigh is drawn upward, while those that flex the leg on the thigh are at the back.
The sartorius arises from the crest of the ilium. It sweeps downward in a sinuous curve across the thigh, in a flattened tendon as it wraps around the inner surface of the knee to its insertion on the tibia.
2 Vastus internus
4 Vastus externus
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