BONES, JOINTS AND LIGAMENTS 



FIG. 29. Fracture of humerus. (Scudder 

 and Cotton.) 



Pivotal joints. Another form of motion in one direc- 

 tion is that permitted by the pivotal joints, in which the 



movement is rotary, 

 as on a pivot. An 

 example of a pivotal 



.Humerus J oint ^ s tnat between 

 the first and sec- 

 ond cervical vertebras, 

 which permits the 

 head to turn from 

 side to side. An- 

 other example is the 

 joint at the elbow 

 end of the radius, 

 which turns as a 

 pivot within a cir- 

 cular ligament at the side of the ulna and thereby 

 allows the palm of the hand to turn either up or 

 down. 



Sliding joints. Other forms of joints, such as those 

 between the articular processes of the vertebras, permit 

 a sliding movement and are therefore called sliding 

 joints. Still others, like the joints between the bodies 

 of the vertebras, allow merely a slight tipping in all 

 directions. In the case of the vertebras, this would seem 

 to be largely a rocking motion upon the pads of elastic 

 cartilage between the bones, rather than a true slip of 

 the joint surfaces. 



Ligaments. The supporting ligaments, which are so 

 important in every joint structure, take the form of a 

 sleeve or capsule, which encloses the ends of the bones 

 and is called the capsular ligament. Besides the capsular 

 ligament, most joints have additional ligaments which 

 strengthen them where necessary. All ligaments con- 



