DISSECTION OF THE UPPER LIMP,. 



Synovial 

 membrane. 



Surface of 

 humerus ; 



of scapula. 



Kinds of 

 movement. 



Flexion and 



extension 



are accom- 

 panied by 

 rotation of 

 scapula. 



Checks to 

 movements, 



Abduction. 



Adduction. 



Circum- 

 duction. 



The synovia! membrane lines tlie articular surface of the capsule, 

 and is continued through the aperture on the inner side to join the 

 bursa beneath the subscapular muscle. The membrane is reflected 

 around the tendon of the biceps, and lines the upper part of the 

 bicipital groove of the humerus. 



Articular surfaces (fig. 38). The convex articular head of the 

 humerus is about three times as large as the hollow of the scapula, 

 and forms rather less than the half of a sphere. The head of the 

 bone is supported on a short neck, which is joined to the shaft at 

 an obtuse angle. 



The glenoid fossa of the scapula is oval in form with the larger 

 end down, and is very shallow. Its margin is slightly more 

 prominent below than above. 



Movements. The looseness of the capsule, the shallowness of the 

 glenoid cavity and its smallness as compared with the extent of the 

 articulating head of the humerus allow of the movements of this 

 joint being both free and extensive. There is the common angular 

 motion in four directions, with the circular or circumductory ; and 

 in addition a movement of rotation. 



In the swinging to and fro movement, the carrying forwards and 

 inwards of the humerus . constitutes flexion ; and the moving it 

 backwards and outwards, extension. Flexion is freer than extension, 

 as the scapula follows the humerus, undergoing a rotation upwards, 

 so that the whole range of movement of the arm in this direction 

 is much greater than that taking place in the reverse articulation. 

 In extension the scapula is similarly rotated downwards, the lower 

 angle approaching the vertebral column. 



Flexion of the humerus upon the scapula is checked by the 

 twisting of the capsule, and by the meeting of the small tuberosity 

 of the former bone with the coraco-acromial arch. Extension is 

 limited mainly by the coraco-huineral ligament. 



Abduction and adduction. In abduction, the arm is moved 

 outwards away from the body ; and in adduction, it is brought 

 downwards to the side. These movements, like the foregoing, 

 are accompanied, and their range is increased by rotation of the 

 scapula. 



When the limb is abducted, the head of the humerus glides 

 downwards in the glenoid cavity, and projects beyond it against 

 the lower part of the capsule, which is stretched ; while the great 

 tuberosity sinks beneath the acromial arch, which sets a limit to 

 the movement. In this condition a little more movement down 

 of the head, either by muscles depressing it or by force elevating 

 the farther end of the bone, will throw it out of place, giving rise 

 to dislocation. 



In adduction, the head of the humerus rises in the socket, and 

 the coraco-huineral ligament being tightened checks the movement. 

 In circumduction, the humerus passes in succession through the 

 four different states above mentioned, and the limb describes a 

 cone, the apex of which is at the shoulder and the base at the 

 digits. 



