SHO ULDER-JOINT 30 1 



An additional ligament, the inferior transverse or spinoglenoid ligament (liya- 

 mentum transversum scapulae inferius), is sometimes found on the scapula, 

 stretching from the outer border of the spine to the margin of the glenoid cavity. 

 When present, it forms an arch under which the suprascapular vessels and nerve 

 pass as they enter the infraspinous fossa. 



Movements. The scapula is capable of being moved upward and downward, forward and 

 backward, or, by a combination of these movements, circumducted on the wall of the thorax. The 

 muscles which raise the scapula are the upper fibres of the Trapezius, the Leva tor anguli scapulae, 

 and the two Rhomboids; those which depress it are the lower fibres of the Trapezius, the Pec- 

 toralis 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 Trape- 

 /ius and Serratus magnus moving the scapula on the wall of the thorax. This mobility is of 

 special importance in ankylosis of the shoulder-joint, the movement of this bone compensating 

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



IV. Shoulder-Joint (Articulatio Humeri) (Figs. 245, 246). 



The shoulder-joint is an enarthrodial or ball-and-socket joint. The bones enter- 

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

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

 of very considerable movement, while the joint itself is protected against dis- 

 placement by the tendons which surround it and by atmospheric pressure. The 

 ligaments do not maintain the joint surfaces in apposition, because when they 

 alone remain the humerus can be separated to a considerable extent from the 

 glenoid cavity; their use, therefore, is to limit the amount of movement. Above, 

 the joint is protected by an arched vault, formed by the under surfaces of the 

 coracoid and acromion processes, and the coracoacromial ligament. The articular 

 surfaces are covered by a layer of hyaline cartilage ; that on the head of the humerus 

 is thicker at the centre that at the circumference, the reverse being the case in 

 the glenoid cavity. The ligaments of the shoulder are the 



Capsular. Transverse Humeral. 



Coracohumeral. Glenoid. 1 



The capsular ligament (capsula articularis) (Figs. 245 and 247) completely 

 encircles the articulation, being attached, above, to the circumference of the 

 glenoid cavity beyond the glenoid ligament, below, to the anatomical neck of the 

 humerus, approaching nearer to the articular cartilage above than in the rest 

 of its extent. It is thicker above and below than elsewhere, and is remarkably 

 loose and lax, and much larger and longer than is necessary to keep the bones 

 in contact, allowing them to be separated from each other more than an inch 

 an evident provision for that extreme freedom of movement which is peculiar 

 to this articulation. Its superficial surface is strengthened, above, by the Supra- 

 spinatus; below, by the long head of the Triceps; behind, by the tendons of the 

 Infraspinatus and Teres minor; and in front, by the tendon of the Subscapularis. 

 The capsular ligament usually presents three openings: One anteriorly, below 

 the coracoid process, establishes a communication between the synovial mem- 

 brane of the joint and a bursa beneath the tendon of the Subscapularis muscle. 



1 The long tendon of origin of the Biceps brachii muscle also acts as one of the ligaments of this joint. See the 

 observations on p. 267 on the function of the muscles passing over more than one joint. 



