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Muscles of the Lower Extremity

thigh, front, fixed, pelvis, knee-joint, attached, bone and thigh-bone

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Muscles of the front of the thigh there are two muscles arising from the front of the back-bone in the lumbar region, and from the hollow of the haunch-bone. They pass over the edge of the pelvic bones to the thigh-bone, and become attached to the small trochanter of that bone, which, as already described (p, 63), is a prominence below the head of the thigh-bone directed inwards. They are called the psoas and iliacus muscles.

The office of these muscles is to bend the hip joint. In other words, if we suppose their place of origin from the bodies of the vertebra to be fixed, by their contraction they will bend the thigh up on the pelvis, or, if the attachment to the thigh-bone be fixed, if the leg be kept stationary, they will bend the body over the thigh. Opposed to the iliacus and psoas is the great mass of muscle that forms the buttocks. The mass is composed of several muscles which arise from the back of the haunch-bone, and are inserted by tendons into the thigh-bone in the neighbourhood of the great trochanter the outer prominence of the thigh-bone. Thus, if the pelvis be fixed, the action of these muscles will extend the hip-joint. That is to say, sup pose the thigh has been bent up on the pelvis, the muscles of the buttock will pull it down and bring it into line with the body. Suppose, however, the legs to be fixed and the body to be bent forwards, then the muscles will act from their attachment to the thigh-bone as the fixed point, and will straighten the trunk, re storing the erect posture. These muscles are, therefore, for this purpose largely developed in man. There are three muscles in particular which compose the mass of muscle referred to. They are called respectively gluteus maximus (Pl. X., jig. 1, 21), which forms the greatest prominence of the region, and whose margin forms the fold of the buttocks, the gluteus medius and gluteus minimus lying below the first, or the greatest, middle sized, and smallest glutei muscles. It is the largest of the three that is the chief extensor, the other two are also abductors of the thigh, that is, they draw the thigh away from the middle line. Associated with them is a number of smaller muscles that pass outwards and across from the pelvic bones to the thigh - bone, whose action is to turn the leg outwards. They are the rotators outwards of the thigh. They also support the hip-joint behind.

To oppose the abducting action of the smaller glutei muscles, there is a group of three muscles called adductors, namely, the adductor mag nus, longus, and brevis (the great, long, and short adductors). They arise from the pubis, the front portion of the pelvic bones, and are attached to the thigh- bone, the first three uniting to occupy the whole rough line on the back of the bone. Being thus inserted at the back of the bone, they rotate it outwards while bringing it to the middle line, and they can also bend the thigh on the pelvis, or the pelvis on the thigh. These muscles are augmented by others which need not be particularized. To summarize, the muscles that pass between the pelvis and the thigh may be divided into the following groups : –I. flexors, passing over the hip-joint in front; II. extensors, placed in the region of the buttocks; III. rotators out wards, passing across between pelvis and femur behind; IV. abductors, also behind; V. adduc tors, in front and to the inside of the thigh.

There still remains a number of muscles attached to the thigh in front and behind. They are separated from the others by the fact that they pass beyond the thigh to be come inserted below the knee-joint, and thus act principally on the knee-joint. They are divisible into two groups—I. flexors of the knee-joint, and II. extensors of the knee joint.

I. The hamstring muscles are the flexors. They are three in number, and all arise from the prominence of the hip-bone (the tuberosity of the ischium) that forms the seat. One of them, called biceps, is attached to the head of the clasp-bone, the outer of the two bones of the leg, and is the outer of the hamstring muscles ; the other two, semitendinosus and semimembranosus, are attached to the shin bone on the inner side of the knee. When the three muscles act from the hip as their fixed point they will bend the knee-joint; and when the knee-joint is fixed they will extend the hip, that is, straighten the trunk. The sar torius, or tailor's muscle (PI. X., fig. 8, s), is a long, slender, ribbon-shaped muscle, which stretches from the upper projecting process of the hip in front across the front of the thigh to the inner side of the knee-joint, where it is attached to the shin-bone. It bends the hip and knee joints, at the same time directing the knee outwards, so producing the posture as sumed by tailors. Hence its name.

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