166 THE ARTICULATIONS OF THE UPPER LIMB. 



directed upwards when the arm is elevated, and the reverse when the arm is depressed. A 

 limited degree of rotation of the clavicle upon its long axis is also permitted, the anterior 

 surface turning 1 upwards as the arm is raised. 1 The movements of the bones are limited, not 

 so much by the forma of the articular surfaces, as by the costo-clavicular and coraco- 

 clavicular ligaments, and the position of the thoracic wall. When the clavicle is forcibly 

 depressed, as in lifting a heavy weight, it presses upon the first rib. its sternal end rises, and 

 the interarticular fibro-cartilage and interclavicular ligament, as well as the anterior and 

 posterior ligaments, are put upon the stretch. The interarticular fibro-cartilage also resists 

 pressure from the shoulder conveyed through the clavicle, and prevents that bone from being 

 displaced inwards. The rhomboid ligament limits upward and backward movements of the 

 clavicle. The acromio-clavicular joint is loose and allows of considerable play, by which the 

 angle between the spine of the scapula and the clavicle is altered as the shoulder is moved ; 

 and the scapula is supported on the clavicle principally by the strong coraco-clavicular 

 ligament, the conoid division of which suspends the scapula from the clavicle, while the 

 trapezoid portion is tightened when the shoulder is pressed inwards. 



LIGAMENTS OF THE SCAPULA. The coraco-scapular or suprascapular liga- 

 ment is a thin, flat band of fibres attached by its extremities to the opposite margins 

 of the notch at the root of the coracoid process, which it thus converts into a foramen 

 for the transmission of the suprascapular nerve, the corresponding artery most 

 commonly passing above it. This ligament is sometimes converted into bone. There 

 is generally a second smaller band below the nerve, close to the bottom of the notch, 

 on the ventral aspect of the bone. 



The coraco-acromial ligament, triangular in shape, is attached by its broader 

 extremity to the outer edge of the coracoid process, and by the narrower to the tip 

 of the acrornion. It consists of strong anterior and posterior bands, with a thinner 

 central part near the coracoid process, where it is sometimes perforated by a 

 prolongation of the tendon of the pectoralis minor. Its inferior surface looks down- 

 wards upon the shoulder- joint, the superior is covered by the deltoid muscle. From 

 its outer border a thin fascial layer is continued downwards over the subacromial 

 bursa and the shoulder-joint. The ligament forms with the coracoid and acromion 

 processes an arch which gives support and protection to the shoulder- joint. 



Spino-g-lenoid lig-ament (fig. 193). This is composed of irregular and lax fibrous 

 bundles which pass from the outer edge of the spine to the back of the head of the scapula, 

 bridging over the suprascapular vessels and nerve as they lie in the acromio-scapular notch. 

 It is often wanting. 



THE SHOULDER-JOINT. 



In this articulation the large and hemispherical head of the humerus is opposed 

 to the much smaller surface of the glenoid cavity of the scapula. The bones are 

 retained in position, not by the direct tension of ligaments, which would restrict 

 too much the movements of the joint, but by surrounding muscles and atmospheric 

 pressure. 



The capsular ligament (fig. 192, 6) is attached to the scapula round the margin 

 of the glenoid cavity, and to the humerus at the place where the neck springs from 

 the tuberosities and shaft. It extends farthest down the humerus on the inferior 

 aspect, and is strongest on the superior aspect. It is so lax that the humerus 

 separates from the glenoid cavity as soon as its muscular connections are detached. 

 Above and behind, the capsule is strengthened by the tendons of the supraspinatus, 

 infraspinatus, and teres minor muscles, which are intimately connected with it as they 

 pass over the joint to reach the great tuberosity of the humerus. In front the tendon 

 of the subscapularis muscle comes into contact with the synovial membrane, which 

 is prolonged upon it through an oval opening in the capsule. The insertion of the 



1 Cleland, Journ. Anat., xviii, 277. 



