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medius, by fleshy fibres, from the dorsum ilii between the anterior and inferior gluteal lines (Fig. 369, p. 415).
This muscle is fan-shaped and its fibres converge to the antero-superior angle
of the greater trochanter, to be inserted into the anterior surface of the trochanter, and sometimes also into the front part of the superior border (Figs. 361, p. 407, and 373). It is also inserted into the capsule of the hip-joint. A bursa is placed deep to the tendon in front of the greater trochanter.
Nerve Supply.The superior gluteal nerve from the sacral plexus (L. 4. 5. S. 1.). .
Actions. The muscle is primarily an abductor of the thigh. Its anterior fibres in addition produce medial rotation and its posterior fibres lateral rotation of the limb.
M. Piriformis.The piriformis is one of the few muscles connecting the lower limb to the
FIG. 372. THE MUSCLES AND NERVES OF THE RIGHT BUTTOCK. The gluteus maximus is reflected; and the gluteus medius is cut, in part, to show the gluteus minimus.
axial skeleton. It arises (1) within the pelvis from the roots of the vertebral arches of the second, third, and fourth sacral vertebræ, and from the adjacent part of the bone lateral to the anterior sacral foramina. Passing out through the greater sciatic foramen, it receives an origin from (2) the upper margin of the
FIG. 373.-MUSCLE-ATTACHMENTS TO THE PROXIMAL ASPECT OF THE GREATER
of the inner surface of the posterior wall of the pelvis
greater sciatic notch of the ilium, and (3) the pelvic surface of the sacro-tuberous ligament.
In the buttock it forms a rounded tendon, which is inserted into a facet on the superior border and medial aspect of the greater trochanter of the femur (Figs. 370, p. 416, and 373).
The piriformis, at its origin, covers part
In the buttock
capsule of the hip-joint,
Nerve Supply. Branches direct from the anterior rami of the first and second sacral
Actions. The muscle is an abductor and lateral rotator of the hip.
M. Obturator Internus. The obturator internus arises on the pelvic aspect of the hip bone, from (1) the whole of the margin of the obturator foramen (except the obturator notch); (2) the surface of the obturator membrane; (3) the whole of the pelvic surface of the hip bone behind and above the obturator foramen; and (4) the parietal pelvic fascia covering it medially.
It is a fan-shaped muscle. Its fibres converge to the lesser sciatic foramen, and end in several tendons, united together, which hook round the margin of the foramen (a bursa intervening), and after passing over the posterior surface of the hip-joint, are inserted into a facet on the medial surface of the greater trochanter of the femur above the trochanteric fossa (Figs. 370, p. 416, and 373, p. 417).
In the pelvis minor the muscle occupies the side wall, covered by the parietal pelvic fascia, which separates it from the pelvic cavity above and the ischio-rectal fossa below. In the buttock the tendon is embraced by the gemelli muscles which are attached to its superior and inferior margins.
The gemelli muscles form accessory portions of the obturator internus.
M. Gemellus Superior.-The superior gemellus arises from the gluteal surface of the ischial spine (Fig. 369, p. 415).
It is inserted into the upper margin and superficial surface of the tendon of the obturator internus muscle.
M. Gemellus Inferior.-The gemellus inferior arises from the superior part of the gluteal surface of the ischial tuberosity (Fig. 369, p. 415).
It is inserted into the inferior margin and superficial aspect of the tendon of
the obturator internus.
Nerve-Supply.-The obturator internus and superior gemellus receive branches from a special nerve, the nerve to the obturator internus from the anterior aspect of the sacral plexus (S. 1. 2. 3.). The inferior gemellus is supplied by the nerve to the quadratus femoris, a branch derived also from the anterior aspect of the sacral plexus (L. 4. 5. S. 1.).
Actions.-The obturator internus and gemelli are abductors and lateral rotators of the hip.
M. Quadratus Femoris. The quadratus femoris arises from the lateral margin of the tuber ischiadicum (Figs. 366, p. 412, and 369, p. 415). It is inserted into the quadrate tubercle and quadrate line of the femur (Fig. 370, p. 416).
The muscle is concealed by the gluteus maximus and the hamstring muscles. Its anterior surface is in contact with the obturator externus muscle and the lesser trochanter of the femur, a bursa intervening. The muscle is not infrequently fused with the adductor magnus.
Nerve-Supply.—A special nerve from the sacral plexus (L. 4. 5. S. 1.) which enters its deep (anterior) surface. Actions. The muscle is an adductor and lateral rotator of the thigh.
THE MUSCLES ON THE POSTERIOR ASPECT OF THE THIGH.
The Hamstring Muscles.
The muscles comprised in this series include the biceps, semitendinosus, and semimembranosus. A part of the adductor magnus, already described, also belongs, morphologically, to this group. They lie in the buttock and posterior aspect of the thigh, and diverge at the knee to bound the popliteal fossa. The origins of the muscles are concealed by the gluteus maximus. In the back of the thigh, enveloped by the fascia lata, they are placed behind the adductor magnus-the semitendinosus and semimembranosus medially, the biceps laterally. The former two muscles help to form the medial boundary of the popliteal fossa, of which the biceps is a lateral boundary.
M. Biceps Femoris.-The biceps femoris has a double origin. (1) Its long head arises, by means of a tendon, in common with the semitendinosus, from the inferior and medial facet upon the sciatic tuberosity (Figs. 366, p. 412, and 369, p. 415) and from the sacro-tuberous ligament. This head, united for a
distance of two or three inches with the semitendinosus, forms a separate fleshy mass, which extends to the distal third of the thigh, to end in a tendon joined by the short head of the muscle. (2) The short head arises separately from, (1) the whole length of the lateral lip of the linea aspera and the proximal two-thirds of the lateral epicondylic line of the femur, and (2) the lateral intermuscular septum. The proximal limit of its origin is sometimes blended with the insertion of the lowest fibres of the gluteus maximus.
The fibres of the short head, directed distally, join the tendon of the long head, and the muscle is inserted (1) into the head of the fibula by a strong tendon, which is split into two parts by the fibular collateral ligament of the knee-joint; (2) by a slip attached to the lateral condyle of the tibia; and (3) along its posterior border by a fascial expansion which connects the tendon with the popliteal fascia.
FIG. 374.-MUSCLE-ATTACHMENTS TO THE RIGHT DORSUM ILII AND TUBER ISCHIADICUM.
There is a bursa between the tendon and the fibular collateral ligament of the knee-joint.
The short head may be absent: there may be an additional origin from the ischium or femur; and the long head may send a slip to the gastrocnemius or tendo calcaneus (Achillis) (tensor fascia suralis).
M. Semitendinosus.-The semitendinosus arises, in common with the long head of the biceps, from the inferior and medial facet upon the ischial tuberosity (Fig. 374, p. 419). Separating from the common tendon, two or three inches from its origin, the muscle forms a long, narrow band which becomes tendinous in the middle third of the thigh.
Passing over the medial side of the knee it spreads out and becomes membranous, and is inserted (1) into the medial side of the body of the tibia just distal to the medial condyle, distal to the gracilis and behind the sartorius (Fig. 376, p. 420), and (2) into the deep fascia of the leg. A bursa separates it from the sartorius superficially, and another, common to it and the gracilis, lies deep to its insertion. The belly of the muscle is marked by an oblique septal tendinous intersection about its middle.
Nerve-Supply. The semitendinosus is supplied by two branches from the nerve to the hamstring muscles (L. 5. S. 1. 2.)
Actions. A flexor of the knee, a medial rotator of the tibia, and an extensor of the hip.
superior and lateral facet on the ischial
PIRIFORMIS P. 419). In the proximal third of the
Becoming tendinous, at the back of the knee, it is inserted into the horizontal groove on the posteromedial aspect of the medial condyle of the tibia (Figs. 376, below, and 384, p. 428). A bursa lies deep to the tendon at its insertion. It has three additional membranous insertions: (1) a fascial band extends distally and medially to join the posterior border of the tibial collateral ligament of the knee-joint; (2) another fascial band extends distally
FIG. 375.-THE MUSCLES ON THE POSTERIOR
FIG. 376.-MUSCLE-ATTACHMENTS TO THE MEDIAL
and laterally, forms the fascia covering the popliteus muscle (popliteus fascia), and is attached to the oblique line of the tibia; and (3) a third strong band extends proximally and laterally to the back of the lateral condyle of the femur, forming the oblique popliteal ligament of the knee-joint.
The membranous origin of the muscle is concealed by the proximal parts of the
semitendinosus and long head of the biceps. The insertion covers the origin of the inner head of the gastrocnemius.
Nerve-Supply. It is innervated by the nerve to the hamstring muscles (L. 5. S. 1. 2.).
Actions. A flexor of the knee, a medial rotator of the tibia, and an extensor of the hip.
Actions of the Muscles of the Thigh and Buttock.
Most of the above muscles act on the pelvis and on the hip- and knee-joints. The psoas major muscle in addition assists in the movements of the vertebral column (p. 411).
1. Movements at the Hip-Joint. The movements of the thigh at the hip-joint are flexion and extension, adduction and abduction, medial and lateral rotation. The following table gives the muscles producing these movements:
2. Movements of the Pelvis on the Thigh. It is to be noted that the several movements tabulated above refer to the movements of the femur at the hip-joint. The contraction of the same groups of muscles produces similar movements of the pelvis on the femur, exemplified in the various changes in the attitude of the pelvis in relation to the thigh and the vertebral column, which occur in locomotion.
3. Movements at the Knee-Joint. The movements at the knee-joint are mainly flexion and extension. Flexion is much more powerful than extension. There is also a limited amount of rotation of the tibia. The movements are produced by certain of the muscles described above, associated with certain of the muscles of the leg.