PELVIC LIMBS 701 



The external and internal borders of the shaft are not distinct, 

 but are rather lines of maximum convexity. The internal border 

 separates the areas of the crureus and vastus interims muscles. The 

 anterior surface is the broadest, and for its upper two-thirds affords 

 an area of origin for the crureus muscle, which arises also on the 

 narrower external surface. The internal surface is covered by the 

 vastus interims muscle. The popliteal space is situated between the 

 lower diverging lips of the linea aspera ; its inner lip is rounded 

 where it is crossed by the femoral artery. 



In the lower extremity, the inner condyle is much longer than the 

 outer condyle, and, when the bone is held vertical, projects further 

 downward. In the natural position in the body, however, the femur 

 is directed downward and inward ; this brings the two condyles level. 

 The lower ends of the two femora are therefore nearer together than 

 the upper ends; in other words, the knee-joints are closer than the hip- 

 joints (Fig. 536). This is necessary in walking in the upright posture 

 in order that the weight of the body may be brought at each step as 

 near as possible to the line of the centre of gravity. In an animal 

 walking with all four limbs this obliquity of the femora is not required 

 (Fig. 537). Compared with the inner condyle, the outer condyle is 

 more prominent in front, and has greater vertical and antero-posterior 

 diameters. Below the flattened epicondyle are a fossa and a groove for 

 the tendon of the popliteus muscle. The inner epicondyle is larger, 

 and bears a well-marked supracondyloid spur for the tendon of the 

 adductor magnus muscle. The inner ridge of the trochlea is higher 

 than the outer ridge. 



THE PATELLA. 



General Description. The Patella is a small, flat bone which 

 lies in front of the knee-joint (Fig. 538). It is a sesamoid bone 

 developed in the tendon of the quadriceps extensor muscle, which 

 arises on the pelvis and femur and, passing in front of the knee-joint, 

 is inserted into the upper end of the tibia. It affords protection to 

 the joint, and increases the leverage of the great extensor muscle of 

 the leg by keeping its terminal tendon as far as possible in front of 

 the joint. 



It resembles in shape and size a small almond (Fig. 539). The 

 blunt end is above and the pointed end is below. It is not quite twice 

 as long as wide, and is compressed from before backward, so that its 



