So great are the changes in surface form of the muscles in different positions of the hip that the iliac crest remains as the one stable landmark. It is a curvc, but being beveled backward, it presents to the side view two lines and almost an angle between them at the top.
The posterior line is marked by two dimples where it joins the sacrum, and the line continues downward irito the fold of the buttocks. From this whole line the gluteus maximus muscle passes down and forward, to just below the head of the thigh bone, making the mass of the buttocks and hip.
Just in front of this, from the top of the crest, descends the gluteus medius muscle, forming a wedge whose apex is at the head of the thigh bone. Between these two muscles is the dimple of the thigh.
Only part of the medius is superficial; its front portion is overlaid by the tensor fasciae femoris muscle, which rises from the edge of the front line of the crest and descends to form with the gluteus maximus the wedge filled in by the medius. The two fasten to the dense plate of fascia that guards the outside of the thigh (ilio-tibial band). This muscle is always prominent and changes its appearance greatly in different positions of the hip, forming a U-shaped wrinkle when the thigh is completely flexed.
On the front end of the crest is a small knob, from which descends the sartorius (tailor's) muscle, longest in the body. It forms a graceful curve as it lies in the groove of the inner side of the thigh, passing to under the knee.
From just below the knob, overlaid therefore by the sartorius, descends the rectus femoris muscle, straight to the knee cap. From the knob, the line continues down and in to the symphysis, marking the boundary between abdomen and thigh.
1 Gluteus medius
2 Gluteus maximus
3 Tensor vaginae femoris
Nature has provided a perfect system of columns, levers and pulleys to which cords and muscles are attached. When contraction takes place, these muscles and their tendons pull, twist or turn, the movable bones. The hip joint is a strictly machine-like contrivance. It has at its connection with the hip, a ball and socket joint and a hinge joint at the knee. The muscles at the hip give a wheel-like movement. Those muscles that pass to the knee parallel the thigh bones to bend the knee.
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