346 THE ARTICULATIONS. 



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 surface of the coracoid and acromion 

 processes, and the coraco-acromial ligament. The articular surfaces are covered by 

 a layer of cartilage : that on the head of the humerus is thicker at the centre than 

 at the circumference, the reverse being the case in the glenoid cavity. The liga- 

 ments of the shoulder are the 



Capsular. Coraco-humeral. 



Glenoid. 1 Transverse humeral. 



The Capsular Ligament 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 move- 

 ment which is peculiar to this articulation. Its superficial surface is strengthened, 

 above, by the Supraspinatus ; below, by the long head of the Triceps ; posteriorly, 

 by the tendons of the Infraspinatus and Teres minor ; and anteriorly, by the ten- 

 don of the Subscapularis. The capsular ligament usually presents three open- 

 ings ; one anteriorly, below the coracoid process, establishes a communication 

 between the synovial membrane of the joint and a bursa beneath the tendon 

 of the Subscapularis. The second, which is not constant, exists between the 

 joint and a bursal sac belonging to the Infraspinatus muscle. ,The third is 

 seen between the two tuberosities, for the passage of the long tendon of the 

 Biceps muscle. 



The Coraco-humeral is a broad band which strengthens the upper part of the 

 capsular ligament. It arises from the outer border of the coracoid process, and 

 passes obliquely downward and outward to the front of the great tuberosity 

 of the humerus, being blended with the tendon of the Supraspinatus muscle. 

 This ligament is intimately united to the capsular in the greater part of its 

 extent. 



The Transverse Humeral Ligament. This is a broad band of fibrous tissue pass- 

 ing from the lesser to the greater tuberosity of the humerus, and always limited to 

 that portion of the bone Avhich lies above the epiphysial line. It converts the 

 bicipital groove into an osseo-aponeurotic canal, and is the analogue of the 

 strong process of bone which connects the summits of the two tuberosities in the 

 musk ox. 



Supplemental Bands of the Capsular Ligament. In addition to the coraco- 

 humeral, the capsular ligament is strengthened by supplemental bands in the 

 interior of the joint. These bands (gleno-humeral ligaments) are situated on 

 the fore part of the capsule, and. the superior passes from the upper part of 

 the anterior margin of the glenoid cavity to the upper end of the bicipital 

 groove. This is sometimes known as Flood's ligament, and is supposed to 

 correspond with the ligamentum teres of the hip-joint. The middle one, from 

 the same origin,' passes downward and outward to the lower part of the lesser 

 tuberosity. Between these two is the orifice of the subscapular bursa. The 

 inferior band passes from the middle of the anterior edge of the glenoid cavity 

 to the under part of the neck of the humerus. The two latter are known as 

 Schlemm's ligaments. 



The Grlenoid Ligament is a fibrous rim attached round the margin of the 



1 The long tendon of origin of the Biceps muscle also acts as one of the ligaments of this 

 joint. See the observations on p. 318 on the function of the muscles passing over more than ont> 

 joint. 



