640 HUMAN ANATOMY. 



Action. — To flex the thigh and extend the leg. Acting from below it will flex 

 the trunk on the hip-joints. 



Relations. — The rectus femoris rests upon the capsule of the hip-joint above 

 and the crureus below. A bursa frequently intervenes between the surface of the 

 ilium and the head which is inserted above the acetabulum. 



3. Vastus Externus (Fig. 610). 



Attachments. — The vastus externus (m. vastus lateralis) arises from the ante- 

 rior intertrochanteric line, the lateral surface of the greater trochanter, and the outer 

 lip of the linea aspera. The fibres curve downward and inward to unite with the 

 crureus and to be inserted into the common tendon. 



Nerve-Supply. — By the anterior crural nerve from the third and fourth lumbar 

 nerves. 



Action. — To extend the leg. 



4. Crureus (Fig. 606). 



Attachments. — The crureus (m. vastus intertnedius) lies below the rectus 

 femoris and between the vastus externus and vastus internus. It arises from the 

 anterior surface of the femur and passes downward into a flat tendon which is inserted 

 into the common tendon a short distance above the patella. 



Nerve-Supply. — By the anterior crural nerve from the third and fourth lumbar 

 nerves. 



Action. — To extend the leg. 



t 



5. Vastus Internus (Fig. 600). 



Attachments. — The vastus internus (m. vastus medialis) is usually so blended 

 with the crureus as to be hardly separable from it. It arises from the spiral line and 

 from the inner lip of the linea aspera of the femur, the fibres curving downward and 

 outward to be partly united with the crureus and partly inse^'ted into the common 

 tendon. 



Nerve-Supply. — By the anterior crural nerve from the third and fourth lumbar 



nerves. 



Action. — To extend the leg. Owing to the oblique direction of the femur 

 downward and inward the action of the quadriceps femoris would be to draw the 

 patella outward as well as upward, thus tending towards an outward dislocation of 

 that bone. This is obviated, however, by the vastus internus, the bulk of whose 

 fibres arise from the lower part of the femur and are directed more or less trans- 

 versely outward to the inner border of the common tendon. 



Relations. — The medial border of the vastus internus forms the outer wall of 

 Hunter's canal (Fig. 606), the fascia which forms the roof of the canal extending 

 across between this muscle and the adductor magnus. 



6. SUBCRUREUS. 



Attachments. — ^The subcrureus Cm. articularis genu) is frequendy so insepara- 

 bly blended with the crureus that it may well be regarded as the deepest layer of 

 the latter rather than as a distinct muscle. It arises from the lower part of the 

 anterior surface of the femur and passes downward to be inserted into the upper 

 border of the capsule of the knee-joint. 



Nerve-Supply. — By the anterior crural nerve from the third and fourth lumbar 

 nerves. 



Action. — To tense the capsule of the knee-joint. 



