44 DISSECTION OF THE ANTERIOR LIMB. 



bones, and may be conceived as having the form of a double-mouthed 

 sack, one mouth being attached around the rim of the glenoid cavity, 

 and the other at the periphery of the head of the humerus. The wall 

 of this sack is comparatively thin, but in front it is strengthened by 

 accessoi-y fibres that pass in a divergent manner from the coracoid pro- 

 cess to the outer and inner tuberosities. These correspond to the 

 coraco-humeral ligament of man. 



Directions. — If, in the removal of the muscles, the ligament has been 

 preserved perfectly intact, it will be noticed that though a considerable 

 force be exerted to pull the articulai- surfaces from each other, they still 

 remain in contact. If, however, an incision be made in the ligament, the 

 air will be heard to rush into the joint, while the bones separate to the 

 extent of half an inch or more. In the shoulder then, as in other joints, 

 atmospheric pressure is to be included among the agents keeping the 

 articular surfaces in contact. The capsular ligament is to be slit up so 

 as to expose the smooth and glistening aspect of the synovial membrane, 

 and the articular surfiices of the bones covered by articular cartilage. 



The Synovial Membrane lines the inner surface of the capsular 

 ligament. It secretes the synovia, or joint oil, some of which will be 

 seen escaping from the joint. 



THE ELBOW-JOINT (PLATE 11, fig. 1). 



This joint is formed by the lower extremity of the humerus and the 

 upper extremities of the bones of the fore-arm. It possesses two lateral 

 ligaments, and an anterior ligament which supports the synovial 

 membrane in front ; but behind, there being no ligament, the synovial 

 sac is directly supported by muscles. 



Movements. — This is a ginglymoid joint, the only movements being 

 Jiexion and extension. In Jiexion, while the humerus remains fixed, the 

 bones of the fore-arm are cai-ried forwards until the movement is arrested 

 by the coi-onoid process passing into the fossa of the same name. In 

 this movement the bones of the fore-arm do not move in the plane in 

 which the humerus lies, but deviate a little outwards. The opposite 

 movement is exten-non, in which the radius and ulna are carried back- 

 wards until they are arrested by the tension of the lateral ligaments, 

 and by the passage of the beak of the olecranon into the fossa of the 

 same name. 



Dirediom. — The anterior and lateral ligaments are to be exposed 

 and defined by removing the muscles from the front of the joint, but on 

 the posterior aspect of the joint the muscles should not be removed at 

 present. 



The External Lateral Ligament is a cord-like band which is fixed 

 superiorly to- a depression on the outer side of the lower extremity of 

 the humerus, and to the ridge which forms the lower boundary of the 



