520 



APPLIED ANATOMY. 



MUSCLES OF THE THIGH. 



There are three main sets of thigh muscles, viz. : extensors, flexors, and adduc- 

 tors. We will limit our consideration to the long muscles. 



Extensor Muscles. The extensor muscles consist of the quadriceps extensor, 



composed of the rectus femoris, vastus 

 internus, vastus externus and crureus 

 (vastus intermedius} , and we might add 

 also the sartori2is. 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 late- 

 ralis) forms the muscular mass on the 

 outer surface of the thigh. A bursa 

 separates it from the gluteus maximus 

 above. Superficially it is readily sepa- 

 rated from the crureus (vastus inter- 

 medius) but blends with it close to the 

 bone. The line separating the two mus- 

 cles 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 , t\\escmitendinosus, 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. 



Rectus femoris 

 with crureus 

 beneath 



Vastus 

 externus 



Vastus 

 internus 



PIG. 529.- The quadriceps extensor muscle of the thigh. 



