ARTHROLOGY 57 



take place in a joint, one surface gliding or moving over another 

 without any angular or rotary movement. 



Angular movement occurs only between the long bones. By 

 it the angle between the two bones is increased or diminished. It 

 may take place in four directions: forward and backward, consisting 

 of flexion and extension; or inward and outward from the medial 

 line of the body, consisting of adduction and abduction. Abduction 

 of a limb is movement away from the medial line of the body. 

 Adduction of a limb is movement toward the medial line of the body. 

 Circumduction is that limited degree of motion which takes 

 place between the head of a bone and its articular cavity, whilst 

 the extremity and sides of the limb are made to circumscribe a 

 conical space, the base of which corresponds with the inferior 

 extremity of the limb, the apex with the articular cavity; this 

 kind of motion is best seen in the shoulder- aind hip-joint. 



Rotation is the movement of a bone upon an axis, which is the 

 axis of the pivot on which the bone turns, as in the articulation 

 between the atlas and axis, when the odontoid process serves as a 

 pivot around which the atlas turns; or else is the axis of a pivot- 

 like process which turns within a ring, as in the rotation of the radius 

 upon the humerus. 



Pronation is a form of rotation in which the inferior extremity 

 of the radius passes before the ulna, and thus causes the hand to 

 execute a kind of rotation from without inward. 



Supination is a form of rotation in which the movement of the 

 forearm and hand are carried outward so that the anterior surface 

 of the latter becomes superior. , 



The Ligamentous Structure. — ^Ligaments are dense, fibrous, con- 

 necting structures. They are made up principally of white fibrous 

 tissue and exist in all true joints. 



There are four kinds of ligaments associated with true joints: 

 The first kind, the capsular ligament which encloses all true 

 joints, is thin and consists of interlaced fibers attached to the bone 

 at the edges of the articular cartilages. It either partly or wholly 

 surrounds the joint, enclosing and protecting a synovial apparatus, 

 which, by secreting a liquid resembling serum, lubricates the joint 

 to prevent friction. 



The second kind, the binding or lateral ligaments, consist of 

 flattened or roimded cords or bands of fibrous tissue. Such a 

 ligament extends from one bone to the other, and firmly attached to 



