34 BONES, JOINTS AND LIGAMENTS 



Hinge joints. Joints which have free motion in but 

 one direction, as in the elbow, the knee and the first and 

 second joints of the fingers, are called hinge joints. 

 Usually in this class of joints, the ends of the bones have 

 more or less perfect ridges which tend to strengthen 

 the joint against any sidewise slip. They also have 

 strong tight ligaments at the sides. 



Knee joint. The knee joint, although classed among 

 the hinge joints, is somewhat complicated by the 



igaments of t>ate!la 

 Cushion of fat 



External semilunar cartilage 

 Anterior crucial ligament 



Articular surface of 



head of tibia 



Posterior crucial ligament 

 Internal semilunar cartilage 



Tendon of a flexor muscle 



Fio. 27. Right knee joint, showing the cartilages and ligaments attached to head 

 of tibia. 



various additional structures necessary to protect and 

 strengthen it, because of its exposed position and the 

 heavy weight which it is called upon to bear. Upon 

 either side are loose pads of cartilage, 1 which serve to 

 cushion the ends of the bones and protect them against 

 side strain. For further protection, the kneecap or 



1 The semilunar cartilages. 



