210 ARTICULATIONS. 



occupies the upper part of the articulation. More rarely, it completely separates 

 the joint into two cavities. 



There are two Synovial Membranes where a complete interarticular cartilage 

 exists ; more frequently, there is only one synovial membrane. 



Actions. The movements of this articulation are of two kinds, x. A gliding 

 motion of the articular end of the clavicle on the acromion. 2. Eotation of the 

 scapula forwards and backwards upon the clavicle, the extent of this rotation being 

 limited by the two portions of the coraco-clavicular ligament. 



3. PROPER LIGAMENTS OF THE SCAPULA. 

 The proper ligaments of the scapula are, the 



Coraco-acromial. Transverse. 



The Coraco-acromial Ligament is a broad, thin, flat band, of a triangular shape, 

 extended transversely above the upper part of the shoulder-joint, between the 

 coracoid and acromion processes. It is attached, by its apex, to the summit of the 

 acromion just in front of the articular surface for the clavicle ; and by its broad 

 base, to the whole length of the outer border of the coracoid process. Its posterior 

 fibres are directed obliquely backwards and outwards, its anterior fibres trans- 

 versely. This ligament completes the vault formed by the coracoid and acromion 

 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 

 Supra-spinatus 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-spinati and Infra-spinati muscles. 



The Transverse or Coracoid Ligament converts the suprascapular notch into a 

 foramen. It is a thin and flat fasciculus, narrower at the middle 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 ; its accompanying vessels above it. 



4. SHOULDER-JOINT. 



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 

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

 verv considerable movement, whilst the joint itself is protected against displace- 

 ment by the strong ligaments and tendons which surround it, and above 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 observed in the glenoid cavity. Its liga- 

 ments are the 



Capsular. Coraco-humeral. 



Glenoid. 



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 than below, 

 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 external surface is strengthened, above, by the Supra- 

 spinatus ; above and internally, by the coraco-humeral ligament ; below, by the 

 long head of the Triceps ; externally, by the tendons of the Infra-spinatus and 



