94 THE UPPER EXTREMITY 



by its position within the capsule, and in the deep sulcus between 

 the tubercles of the humerus, serves to keep the head of 

 the bone in place, and to steady it in the various movements 

 at the shoulder-joint. 



The stratum synoviale (the synovial membrane) lines the 

 capsule of the joint, and is reflected from it upon the anatomical 

 neck of the humerus as far as the articular margin of the 

 head of the bone. The bursal protrusion of the bursa sub- 

 scapularis under the tendon of the subscapularis muscle has 

 already been noticed. The tendon of the biceps, as it 

 traverses the joint, is enveloped in a tubular sheath of 

 the membrane, which bulges out through the opening of the 

 capsule in the form of a bursa, which lines the sulcus inter- 

 tubercularis, and receives the name of bursa intertubercularis. 



Articular Surfaces. The smooth, glistening articular 

 cartilage, which coats the head of the humerus, is thickest 

 in the centre, and thins as it passes towards the edges. In 

 the case of the glenoid cavity the reverse of this will be 

 noticed. The cartilaginous coating is thinnest in the centre, 

 and becomes thicker as it is traced towards the circumference. 



Movements at the Shoulder -joint. The shoulder is a ball-and-socket 

 joint (enarthrosis), and consequently movement in every direction is per- 

 mitted, viz. (\) flexion, or forward movement ; (?.} extension, or backward 

 movement (checked in its extent by the coraco-humeral ligament) ; (3) 

 abdiiction, or lateral movement (checked by the coraco-acromial arch) ; (4) 

 adduction, or medial movement (limited by the coraco-humeral ligament). 

 In addition to these different forms of angular movement, rotation to the 

 extent of a quarter of a circle and circumduction are permitted. 



The muscles chiefly concerned in producing these movements are : 

 flexion the pectoralis major and the anterior part of the deltoid ; extension 

 latissimus dorsi, posterior part of the deltoid, and the teres major ; 

 abduction the deltoid and supraspinatus ; adduction pectoralis major, 

 coraco-brachialis, teres major, and latissimus dorsi ; rotation medially 

 subscapularis, pectoralis major, latissimus dorsi, teres major ; rotation 

 laterally supraspinatus, infraspinatus, and teres minor ; circumduction is 

 produced by the action of different combinations of these muscles. 



FOREARM AND HAND. 



Dissection. The skin has already been removed from the volar and dorsal 

 surfaces of the forearm. It should now be raised from the dorsum of the 

 hand by making incisions along the radial and ulnar borders. This is 

 done in order that the superficial structures in this region may be examined 

 in connection with those of the forearm. 



Venae Superficiales (Superficial Veins). On the dorsum of 



