This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The extensor muscles consist of the quadriceps extensor, composed of the rectus femoris, vastus internus, vastus externus and crureus (vastus intermedins), and we might add also the sar'torius. The quadriceps of the thigh is homologous with the triceps extensor of the arm, the fourth head of the latter muscle being the anconeus. The sartorius normally has no homo-logue in the upper extremity, but is sometimes represented by a slip from the latissimus dorsi to the triceps (dorsi-epitrochlearis - Macalister). The rectus arises by an anterior or straight head from the anterior inferior spine of the ilium and a posterior or reflected head from the upper surface of the rim of the acetabulum. The tendon formed by the union of these two heads passes downward directly over the head of the femur and, in operating on the joint from in front, it must be deflected to one side. The belly of the muscle is separate and not attached to the other muscles (Fig. 529).
The vastus externus (vastus lateralis) forms the muscular mass on the outer surface of the thigh. A bursa separates it from the gluteus maximus above. Superficially it is readily separated from the crureus (vastus inter-medius) but blends with it close to the bone. The line separating the two muscles is directly upward from the outer edge of the patella. The vastus internus (vastus medialis) arises from the inner edge of the linea aspera as high up as the lesser trochanter. Its outer edge blends with the crureus.
The sartorius in the middle third of the thigh lies directly over Hunter's canal. It inserts into the tibia below and internal to its tubercle, hence it spans both the hip-joint and knee-joint. It flexes the thigh on the pelvis and the leg on the thigh. It also rotates the thigh outward and the leg inward especially when the latter is flexed.
The flexor muscles, also called the hamstring muscles, comprise the biceps cruris, the semitendinosus, and the semimembranosus. The short head of the biceps arises from the outer lip of the linea aspera. Above, the long head is blended with the semitendinosus and arises from the great sacrosciatic ligament and the lower inner part of the tuberosity of the ischium.
Fig. 529. - The quadriceps extensor muscle of the thigh.
The semimembranosus arises from the tuberosity just above and external to the biceps and semitendinosus. The biceps, arising by its long head from the tuberosity, lies first to the inner side of the sciatic nerve, and then, as it crosses obliquely to reach the outer side of the knee, covers the nerve and finally lies to its outer side. The upper portion of the semimembranosus lies beneath both the long head of the biceps and the semitendinosus, and only comes to the surface between them from the middle of the thigh down. The tendons of the semimembranosus and semitendinosus form the inner hamstring tendons and the biceps the outer hamstring tendon (Fig. 530).
Fig. 530. - The flexor muscles of the thigh.
Fig. 531. - Adductor muscles of the thigh.
The adductor muscles are the adductor brevis, adductor longus, adductor magnus, and gracilis; for clinical purposes the pectinezis may also be included, although it is morphologically simply a detached portion of the iliacus. The quad-ratus femoris and obturator externus belong morphologically to the adductor group, but from a clinical standpoint they are associated more with the external rotators of the hip than the adductors of the thigh. The adductor muscles separate the flexor and extensor groups on the inner side of the thigh. The adductor longus arises by a strong tendon from the body of the pubis just below its spine and inserts into approximately the middle third of the femur in the linea aspera (Fig. 531). When the thigh is abducted the tense edge of its tendon is evident, and if followed upwards it leads to the spine of the pubis. It lies on the same plane as the pectineus, which is immediately above; sometimes, especially in the female, an interval exists between the two through which the adductor brevis may be visible. Near its insertion it forms part of the floor of Scarpa's triangle and the upper part of the floor of Hunter's canal.
The adductor brevis arises from the descending ramus of the pubis just below the origin of the adductor longus and inserts into the femur from the lesser trochanter to the linea aspera. It lies directly behind the upper portion of the adductor longus and in front of the adductor magnus.
The adductor magnus arises from the ramus of the ischium, from the adductor brevis in front to the hamstring tendons on the tuberosity behind. It is inserted into nearly the whole length of the linea aspera, and by a distinct tendinous band into the adductor tubercle at the upper edge of the internal condyle. Its upper portion is sometimes called the adductor minimus. It is pierced near the bone by the pe*r-forating branches of the profunda femoris artery and near its lower portion by the femoral artery and vein. It forms part of the floor of Hunter's canal. Its homologue in the upper extremity is the coracobrachialis muscle.
The gracilis arises from the pubis just to the inner side of the adductor brevis and passes straight down the thigh to insert into the tibia, beneath the sartorius and above the semitendinosus. It is sometimes represented in the upper extremity by a slip from the lower border of the pectoralis major called the chondro-epitrochlearis.
The pectineus arises from the iliopectineal line to insert just behind and below the lesser trochanter. It lies on the same level as the adductor longus and just above it.
If the thigh is flexed and rotated outward the sartorius is seen crossing it obliquely, and Scarpa's triangle is evident as a depression downward from Poupart's ligament. The muscular mass of the upper inner portion of the' thigh is composed of the gracilis and adductor muscles. Immediately above the patella is the flat tendon of the rectus, and above and to the inner side of the patella is a rounded mass formed by the vastus internus (Fig. 532). Running upward and inward from the outer edge of the patella to the middle of the thigh is a groove which separates the rectus and vastus externus. On the outer side a flat groove is formed by the iliotibial band of the fascia lata. At its posterior border is the external intermuscular septum between the vastus externus and biceps.