150 AETICULATIOXS OF THE UPPER LIMB. 



t];ie cavity. The upper part of it is connected with the tendon of the 

 long head of the biceps muscle, which is also fixed into the upper part 

 of the glenoid fossa, within the ca]3sule of the joint. 



The" sjrnovial membrane is reflected uninterruptedly from the 

 margin of the glenoid cavity on the inner surface of the fibrous ca])- 

 suleto the humerus, but its form is complicated by its relation to the 

 tendons of the biceps and subscapularis muscles. The long tendon of 

 the biceps muscle traversing the joint in its course from the upper 

 border of the glenoid cavity to the bicipital groove, is enclosed in a 

 tubular sheath, formed by an offset or process of the synovial mem- 

 In-ane, which is continued down upon it beyond the fibrous capsule into 

 the bicipital groove, and is thence reflected upwards upon it to its 

 origin, where it again becomes continuous with the synovial mem- 

 brane of the capsule in such a manner as to preserve the integrity of 

 the membrane. The bursal prolongation of the synovial membrane on 

 the tendon of the subscapularis muscle is of variable extent, sometimes 

 scarcely existing, sometimes forming a considerable pouch on the venter 

 of the sca})ula. 



Subacromial Bursa. — Superficial to the muscles covering the 

 top of the joint is a considerable bursa mucosa, by means of which 

 the contiguous surfaces of the coracoid and acromion processes, 

 and of the coraco-acromial ligament and deltoid muscle, are lubri- 

 cated, so as to facilitate the movements of the subjacent head of the 

 humerus. * 



Movements.- — Great freedom of movement of the humerus in eveiy direction 

 is admitted at the shoulder-joint ; but superiorly and j^^osteriorly the extent of 

 the movement is somewhat limited by the margin of the acromion. "When the 

 arm is raised the great tiiberosity of the humerus becomes locked against the 

 acromion as soon as the position is reached in which the limb lies at right angles 

 to the trunk, and all further elevation is accomplished by movements in the 

 stemo-clavicular and acromio-clavicular articulations. The arch fonned by the 

 acromion, the coracoid process, and the deltoid ligament, lined by the sub- 

 acromial bursa, forms a sort of secondary socket in which the extremity of the 

 humerus, covered by the tendons inserted into the great tuljerosity. revolves, and 

 against which it is pressed when the weight of the body is made to rest upon the 

 arms. 



ARTICULATIONS OF THE FOREARM AND ELBOW. 



The bones of the forearm are united by a superior and an inferior 

 articulation and an interosseous membrane. 



In the SUPERIOR radio-ulxar articulation the head of the radius is 

 connected with the small sigmoid cavity of the ulna by the annular 

 or orbicular ligament. This ligament is a strong band of fibres 

 attached to the ulna in front and behind, at the extremities of the small 

 sigmoid cavity, and forming four-fifths of a ring which encircles the 

 head of the radius and binds it firmly in its situation. The_externa[ 

 lateral ligament of tlie elbow is inserted into its outer surface ; its deep 

 surface is smooth, and is lined by the synovial membrane of the elbow- 

 joint. 



The INFERIOR RADio-ULNAR ARTICULATION. — The connection between 

 the semilunar surface of the radius and the lower end of the ulna is 

 effected by means of a fibro-cartilage, a synovial membrane, iind some 

 scattered ligamentous fil)res in front and behind. The triangular fibro- 



