Muscles of the Hips and Lower Limbs
Hip & Thigh
Like the forearm, the upper leg, or thigh, has a dense arrangement of many muscles. On the anterior side, the most prominent of the muscles are the sartorius muscle and the four muscles that make up quadriceps muscle group (the “quads”).
The quadriceps sounds like it should be just one muscle, akin to the triceps brachii (one muscle with three heads), but it is a group of four separate muscles, three visible on the surface, and the fourth obscured. The three surface muscles of the quadriceps are the rectus femoris in the center, the vastus medialis on the medial side, and the vastus lateralis on the lateral side. Deep to rectus femoris and largely hidden by it is the vastus intermedius. The four muscles of the quadriceps all extend the leg (knee to ankle), and the rectus femoris additionally can flex the thigh at the hip. The sartorius muscle is a distinctively long and thin muscle that crosses the thigh diagonally. Sartorius comes from the Latin for "tailor," and this is sometimes called the tailor’s muscle, although the reasons for the nickname are obscure. It may be because the shape of the muscle is thin and long, like a tailor’s measuring tape; it may be because it is close to the inseam a tailor measures when tailoring pants, or it may be because it helps bring about the cross-legged position that tailors often adopt when working.
There are three layers of gluteal muscles on the posterior hips, just like there are three layers of muscles in the abdominal trunk. The largest of them is the most superficial muscle, the gluteus maximus. Its origin is on the ilium of the coxal bone, and it inserts part-way down the shaft of the femur. It helps maintain erect posture, abducts the thigh, and rotates the thigh outward. Below the gluteus maximus is the smaller gluteus medius. The gluteus medius muscle helps abducts the thigh along with the gluteus maximus, but can rotate the thigh inward where the gluteus maximus rotates the thigh outward. The below the gluteus medius are several muscles, one of which is the gluteus minimus, the smallest of the gluteal muscles. It is a synergist for the gluteus medius.
In the posterior thigh the bulk of the musculature is made up of three long muscles that are collectively called the "hamstrings." The origin of this nickname is obscure, but it may have to do with the practice of butchers of hanging the thighs of butchered animals such as pig (the “hams”) by the tendons of these three muscles. From the medial edge to the lateral edge of the posterior thigh, the hamstring muscles are the semimembranous muscle, the semitendinosus muscle, and the biceps femoris muscle. Notice the upper leg has a “biceps” muscle just like the upper arm does. This is why you have to indicate which biceps you are taking about when discussing one or other of these muscles. On the medial edge of the posterior thigh is the gracilis muscle (inner thigh). It is also visible on the medial edge of the thigh from the anterior.