94 



Anatomy of Skeleton 



The more posterior fibres, on the other hand, are relaxed on extension, and do not 

 seem to be of much value as strengthening the joint : their position and direction 

 make a ligamentous groove or concavity with the more prominent front band, into 

 which the ulnar nerve passes from the back of the condyle (see Fig. 76). 



The external lateral ligament radiates from the outer condyle, for the most pu.rt 

 to decussate with and join the orbicular fibres, but some of its anterior and posterior 

 fibres reach the coronoid and olecranon respectively : the posterior group is of especial 

 importance, for this is attached to the external condyle (Figs. 68 and 72) in the line 

 of the axis of movement, so that it is also in a state of tension. It is a well-marked 

 set of fibres, passing from the condyle to the strong ridge on the ulna running from 

 the olecranon along the back of the lesser sigmoid cavity, and for a little distance 



below this on the prominent rim of the tri- 

 angular area below the cavity : it is partly 

 fused with the orbicular ligament, and 

 accounts for the greater length of the 

 posterior border of the lesser sigmoid notch 

 (Fig. 72). 



The upper end of the radius is on the 

 whole in front of the plane of the ulna : 

 its head is against the coronoid process, 

 but the ulna is bowed backwards below 

 this prominence, and this, in conjunction 

 with the presence of the olecranon and 

 heavy shaft below the olecranon, gives the 

 radius its rather anterior position : the 

 articular surfaces for the two bones on the 

 FIG. 73. inner aspect of elbow-joint. Note humerus are nearly on the same level, but 



the strong anterior band from front of , -.. .. , .., , 



inner condyle to inner tubercle on coronoid the radlUS articulates With that bone by 



process. This stands away from the posterior the upper surface of its head, whereas the 



fibres, thus making a concavity in which the . . , . . , 



ulnar nerve lies. ulna carries its articular surface on its front 



aspect. When the forearm is pronated, the 

 radius turns over the front of the ulna altogether, with the exception of its head. 



This movement takes place round an axis that can be drawn, for practical pur- 

 poses, from the middle of the head of the radius to that of the ulna, just outside the 

 base of its styloid process, as shown in Fig. 74. 



ULNA. 



Observe the groove that crosses the floor of the great sigmoid notch, separating 

 the olecranon and coronoid : the articular cartilage is also interrupted here by a line 

 of fibrous tissue. At each end of the groove is a notch in the margin, bridged on the 

 inner side by the transverse fibres of the lateral ligament, but covered in externally 

 by the outer ligament, which may, however, show a slight deficiency here (Fig. 72) 

 for vessels and fatty tissue. 



The smooth central ridge that runs down the sigmoid notch corresponds with the 

 hollow of the trochlea, and, in further correspondence, we find that the outer moiety 

 of the notch thus divided is greater on the olecranon and smaller on the coronoid : 

 compare with a humerus. 



.post, fibres 

 ant. band 



transverse or 

 >Uique fibres 



Olecranon.- - Upper surface (Fig. 75) from its margin backwards presents synovial, 

 ligamentous, bursal, and tendinous areas. Its posterior surface has a broad, triangular 



