ARTICULATIONS OF THE UPPER EXTREMITIES. 287 



Of the Scapula-Humeral Articulation. 



The glenoid cavity of the scapula, and the head of the os 

 humeri form this joint. As usual, each articular surface is 

 covered with cartilage, of which that on the os humeri is thick- 

 er in the middle than near its circumference, while the reverse 

 occurs on the scapula. From the shallowness of the glenoid 

 cavity and the much greater size of the head of 'the os humeri, 

 but very few points of their opposed surfaces can come into 

 contact at the same moment, though they may all do so in suc- 

 cession: hence, a considerable portion of the head of the os hu- 

 meri is always against the capsule of the joint. The remaining 

 parts of this articulation are the capsular ligament, the synovia! 

 membrane, and the glenoid ligament. 



The capsular ligament invests completely this joint, though it 

 is thinner in some places than at others. It arises from the mar- 

 gin of the glenoid cavity, and is inserted into the neck of the os 

 humeri, including a larger space of the neck below, than it does 

 above. The tendons of the muscles whrich arise from the ex- 

 ternal and internal surface of the scapula, to be inserted into 

 the tuberosities of the os humeri, as they approach their points 

 of insertion adhere very closely to the capsular ligament, and 

 are, indeed, more or less blended with it. Bichat' considers, 

 that the tendon of the sub-scapularis muscle supplies the place 

 of the capsular ligament entirely at its lower part. This liga- 

 ment is formed by fibres, which are very much intermixed with 

 one another, arid have a greater degree of thickness above than 

 below, or, indeed, at any other point. The former is due to a 

 thick fasciculus, the Coraco-Humeral Ligament, also called by 

 some Ligamentum Adscititium, which takes its origin from the 

 posterior and external margin of the coracoid process, and pro- 

 ceeding beneath the triangular ligament to the upper part of the 

 os humeri, joins the capsular ligament, and adheres very firmly 

 to it. This ligament keeps the head of the os humeri on its 

 proper level in regard to the glenoid cavity; but the moment it 

 is cut, the length of the capsular ligament permits the head of 

 the os humeri to fall about an inch, and, indeed, to suffer a par- 

 tial dislocation. The strength of the joint however depends 



