THE ULNA. 



89 



natural skeleton it is not in contact with the carpal bones, being sepa- 

 rated from tlie cuneiform bone by an iuterarticular fibro-cartilage. 



The superior rxtrcmifij is of large size, and presents for articulation 

 with the humerus a large articular surface, the fp'eat sigmoid cavity, 

 which looks forwards and is bounded in its posterior and upper part by 

 the olecranon, a thick process continued upwards from the shaft, and 

 in its lower part by the coronoid process, which projects forwards. 

 The great sigmoid cavity is concave from above downwards, and is 

 convex from side to side, being traversed by a vertical ridge. The part 

 external to this ridge is broad and convex above, while the part internal 

 to the ridge is broad and concave below : a slight constriction, and 



Fig. 75. — Eight Ulxa from before. 



Fig. 76. — Right Ulxa from behind. (A. T.) 3 



1, point or beak of the olecranon ; 2, tuberosity of 

 the olecranon ; 3, end of the coronoid process ; 4, 

 great sigmoid articular surface ; 5, lesser sigmoid 

 cavity, and lielow it the surface for the supinator 

 brevis muscle ; 6, interosseous ridge ; 7, lower 

 extremity or head ; 8, styloid process ; 9, rough 

 surface of insertion of the brachialis anticus 

 muscle; below 10, the oblicpie line' marking the 

 attachment of the pronator quadratus muscle ; 11, 

 triangular surface for the anconeus muscle ; 12, 

 upper part of the posterior border, to the right of 

 which the depressions for the long extensor muscles 

 of the fingers occux^y the posterior surface. 



sometimes a notch of division occurs 

 across the middle of the cavity. Con- 

 tinuous with the great is the s^mall sig- 

 moid cavity, a small articular surface on 

 the outer side of the base of the coronoid 

 process, slightly concave from before back- 

 wards, and articulating with the cylin- 

 drical part of the head of the radius. 

 Superiorly the olecranon is broad and un- 

 even, terminating in front in an acute 

 process or beak, which overhangs the 

 great sigmoid cavity, and which in exten- 

 sion of the elbow passes into the olecranon 

 fossa of the humerus, and behind in a 

 rectangular prominence or tuberosity, 

 which forms the point of the elbow, and 

 gives attachment to the triceps extensor muscle. The posterior surface 

 of the olecranon is subcutaneous and oonti-nuous with the posterior 

 margin of the shaft of the ulna. The extremity of the coronoid process 

 is sharp and prominent, and is received during flexion into the 

 coronoid fossa of the humerus •. its superior surface forms part of the 

 surface of the great sigmoid cavity ; the inferior surface rises gra- 

 dually from the anterior surface of the bone, and is covered by a large 

 triangular roughness which gives insertion to the brachialis anticus 

 muscle. 



The lody or slaffl in the upper three-fourths of its extent is three- 



