THE SHOULDER-JOINT. 



345 



processes for the protection of the head of the humerus. It is in relation, above, 

 with the clavicle and under surface of the Deltoid ; below, with the tendon of the 

 Supraspinatus muscle, a bursa being interposed. Its anterior border is continuous 

 with a dense cellular lamina that passes beneath the Deltoid upon the tendons of 

 the Supra- and Infraspinatus muscles. This ligament is sometimes described as 

 consisting of two marginal bands and a thinner intervening portion, the two 

 bands being attached respectively to the apex and base of the coracoid process, 

 and joining together at their attachment into the acromion process. When the 

 Pectoralis minor is inserted, as sometimes is the case, into the capsule of the 

 shoulder-joint, instead of into the coracoid process, it passes between these two 

 bands, and the intervening portion is then deficient. 



The Transverse or Coracoid (stiprascapular] Ligament converts the suprascapu- 

 lar notch into a foramen. It is a thin and flat fasciculus, narrower at the mid- 

 dle than at the extremities, attached by one end to the base of the coracoid 

 process, and by the other to the inner extremity of the scapular notch. The 

 suprascapular nerve passes through the foramen ; the suprascapular vessels pass 

 over the ligament. 



Movements of Scapula. The scapula is capable of being moved upward and 

 downward, forward and backward, or, by a combination of these movements, cir- 

 cumducted on the wall of the chest. The muscles which raise the scapula are the 

 upper fibres of the Trapezius, the Levator anguli scapulae, and the two Rhom- 

 boids ; those which depress it are the lower fibres of the Trapezius, the Pectoralis 

 minor, and, through the clavicle, the Subclavius. The scapula is drawn backward 

 by the Rhomboids and the middle and lower fibres of the Trapezius, and forward 

 by the Serratus magnus and Pectoralis minor, assisted, when the arm is fixed, by 

 the Pectoralis major. The mobility of the scapula is very considerable? and 

 greatly assists the movements of the arm at the shoulder-joint. Thus, in raising 

 the arm from the side the Deltoid and Supraspinatus can only lift it to a right 

 angle with the trunk, the further elevation of the limb being effected by the 

 Trapezius moving the scapula on the wall of the chest. This mobility is of special 

 importance in ankylosis of the shoulder-joint, the movements of this bone com- 

 pensating to a very great extent for the immobility of the joint. 



^ IV. Shoulder-Joint (Fig. 243). 



The Shoulder is an enarthrodial or ball-and-socket joint. The bones entering 

 into its formation are the large globular head of the humerus, which is received 



BICEPS. 

 CORACO ACROMIAL ', GLENOID LIGAMENT. 



LIGAMENT. ', / 



DELTOID _!_ 



SUPRA 

 SPINATUS. 



DELTOID. SUPRA SPINATUS. 



^SUB- 

 SCAPULA mS. 



Y ^i 



/ i 



TERES MAJOR. Circumflex vessels. 



BSCAPULARIS. 



CircumHejc ressds. 



FIG. 244. Vertical sections through the shoulder joint, the arm being vertical and horizontal. (After 



into the shallow glenoid cavity of the scapula an arrangement which permits of 

 very considerable movement, whilst the joint itself is protected against displacement 



