266 



ADVANCED PHYSIOLOGY 



designed to make the movements of the bones upon each 

 other smooth and free, with the least possible friction. 



The bones are bound together by tough bands called liga- 

 ments. At the knee joints there are several (Fig. 134); 

 there is a pair of short ones, the crucial ligaments, run- 

 ning directly between the ends of the bones and crossing each 

 other like the parts of a letter X. More important are those 

 outside of the joint and extending over it from one bone to 

 the other. On either side there is a lateral ligament, attached 



to the femur and 

 extending down to 

 the sides of the upper 

 parts of the tibia and 

 fibula. Another, the 

 posterior ligament, at 

 the back of the joint, 

 is attached to the 

 same bones. The 

 anterior ligament (in 

 front) is different 

 from the others in 

 having in the middle, 

 a rounded, flat disc 

 of bone, called the 

 knee cap, or patella, 

 strengthening the 

 joint and protecting 

 the more delicate 

 parts within from injury. There is another, rather irregular 

 ligament, called the capsular ligament, larger than the others 

 and partly covering them all, like a sac wrapped around the 

 bones and fastened to the lower end of the femur and the 

 upper end of the tibia. 



The other hinge joints in the body differ from that at the 

 knee only in slight details. The exact position and number 



FIG. 134. THE KNEE JOINT 



A shows the exterior ligaments. B shows the joint 



with the external parts removed. (Thompson) 



