96 



DISSECTION OF THE UPPER LIMB. 



Anterior 

 ligament. 



Posterior 

 ligament. 



Dissection. 



Synovial 

 membrane. 



Lower end 

 of the 

 humerus : 



two articu- 

 lar surfaces. 



and three 



Upper end 

 of the ulna. 



Head of the 

 radius. 



Kinds of 

 motion : 



bending ; 



the humerus. The fibres diverge, and are inserted in this way : 

 The anterior, which are the strongest, are fixed to the edge of the 

 coronoid process ; the posterior are attached to the side of the 

 olecranon ; and a few middle fibres join a band passing transversely 

 over the notch between the olecranon and the coronoid process. The 

 ulnar nerve is in contact with the ligament ; and vessels enter the 

 joint by the aperture beneath the transverse band. 



The anterior ligament is thin, and its fibres are separated by 

 intervals in which masses of fat are lodged. By its upper edge 

 the ligament is attached to the front of the humerus, and by its 

 lower to the front of the coronoid process and the orbicular 

 ligament of the radius. The brachialis aiiticus muscle covers it. 



The posterior ligament is much thinner and looser than the 

 anterior, and is covered completely by the triceps muscle. 



Superiorly it is attached to the humerus above the fossa for the 

 olecranon ; and inferiorly it is inserted into the olecranon. Some 

 few fibres are transverse between the margins of the fossa before 

 mentioned. 



Dissection. Open the joint by an incision across the front near 

 the humerus, and disarticulate the bones, in order that the articular 

 surfaces may be seen. 



The synovial membrane of the joint passes from one bone to 

 another along the deep surface of the connecting ligaments. It is 

 continued downwards on the inner surface of the orbicular ligament, 

 and serves for the joint of the head of the radius with the small 

 sigmoid cavity of the ulna. 



Articular surfaces. The articular surface of the lower end of 

 the humerus is divided into two parts for the bones of the forearm. 

 That for the radius, on the outer side, forms a rounded eminence 

 (capitellum) which is confined to the front of the bone. The 

 surface in contact with the ulna (trochlea) is limited internally 

 and externally by a prominence, and hollowed out in the centre. 

 On the front of the humerus above the articular surface are two 

 depressions which receive the coronoid process of the ulna and the 

 head of the radius during flexion of the joint; and on the posterior 

 aspect is a large fossa for the reception of the olecranon in extension 

 of the joint. 



On the end of the ulna the articular surface of the great sigmoid 

 cavity is narrowed in the centre, but expanded above and below 

 (fig. 40). A median ridge, which is received into the hollow of 

 the trochlea, extends from the upper to the lower end of the fossa ; 

 and across the bottom of the cavity the cartilage is wanting over a 

 small space between the coronoid and olecranon processes. 



The head of the radius presents a circular depression with a 

 raised margin, which plays over the capitellum of the humerus. 



Movement. This joint is like a hinge in its movements, per- 

 mitting only flexion and extension. 



In flexion, the bones of the forearm move forwards, each on its 

 own articular surface, so as to leave the back of the humerus 

 uncovered. The movement is checked by the meeting of the arm 



