THE ULNA. 95 



extremity, a fibrous band, giving origin to the pronator radii tcres muscle, descends to the 

 internal condyle, and through the arch thus formed passes the median nerve, accompanied 

 frequently by the brachial artery, or by a large branch rising from it. This process represents 

 a portion of the bone enclosing a foramen in many animals. (Struthers, Edin. Med. Journ., 

 1848; Gruber, <; Can. supracond. humeri," Mem. Acad. Imp. St. Petersburg, 1859.) The thin 

 plate between the olecranon and coronoid fossae is sometimes perforated, forming the supra- 

 trocltlear or intercondylar foramen. 



THE ULNA. 



The ulna is the internal of the two bones of the forearm, and is longer than the 

 radius by the extent of the olecranon process. It is inclined downwards and out- 

 wards from the huinerus in such a direction that a straight line passing from the 

 great tuberosity of the humerus downwards through the capitellum would touch the 

 lower end of the ulna. 



The ulna articulates with the humerus and the radius : in the natural skeleton it 

 is not in contact with the carpal bones, being excluded from the wrist-joint by an 

 interarticular fibre-cartilage. 



The superior extremity is much the larger, and articulates with the humerus 

 by means of the great sigmoid cavity, which looks forwards and upwards, 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 projecting 

 forwards. The great sigmoid cavity is concave from above downwards, and traversed 

 by a longitudinal ridge. The part external to this ridge is broad and convex above, 

 while the part internal to the ridge is concave and broader below : a slight 

 constriction, and sometimes a groove of division, occurs across the middle of the 

 cavity. Continuous with the great is the small sigmoid cavity, a small articular 

 surface on the outer side of the base of the coronoid process, concave from before 

 backwards, for the reception of the head of the radius. Superiorly, the olecranon is 

 broad and uneven, terminating in front in an acute process or bealc, which overhangs 

 the great sigmoid cavity, and which in extension 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 

 continuous 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 or anterior surface rises gradually from the anterior 

 surface of the bone, and is covered by a large triangular roughness, the inner part 

 of which, together with the tuberosity of the ulna at the lower angle of the surface, 

 gives insertion to the tendon of the brachialis anticus muscle. 



The body or shaft tapers from above downwards, and in the upper three-fourths 

 of its extent is three-sided, and slightly curved with the convexity backwards ; in 

 the lower fourth it is slender and more cylindrical. It also presents a lateral curve, 

 with the concavity inwards above, outwards below. The anterior border, continued 

 downwards from the inner edge of the coronoid process, is thick and rounded. The 

 posterior border begins a little below the olecranon process by the meeting of two 

 lines which limit the triangular subcutaneous surface of the upper end of the bone, 

 and runs with a sinuous course to the back of the styloid process : it is smooth and 

 prominent in the upper two-thirds, rounded and ill defined in the lower third. The 

 external border is in the middle three-fifths of the shaft a sharp rough edge which 

 gives attachment to the interosseous membrane ; in the lower fifth it is only a 

 faintly marked line. In the upper fifth this border is continued by two lines, one 

 passing into the inner margin of the coronoid process, and the other to the posterior 

 extremity of the small sigmoid cavity, near which it becomes very prominent as the 



