Limbs : Upper Limb 89 



its tendon is carried out (away from the short head, which is fixed to the coracoid 

 process) and the small tuberosity becomes apparent, covered of course by the Sub- 

 scapularis tendon. The articular head can be felt through this tendon by passing the 

 fingers up into the axilla, and its direction and continuity with the rest of the bone 

 demonstrated by rotation : when there is wasting of the muscles, the relation of the 

 head to the line of the axillary border of the scapula can also be appreciated. Examine 

 from the front, by rotating the arm, the position of the head with reference to the 

 coracoid process, which is just internal to it. The shaft of the bone can be palpated 

 better from the sides than from the front or back, owing to the thickness of muscles 

 on these aspects. The shaft is easily felt just below the insertion of the Deltoid, and 

 the external supra-condylar ridge is directly palpable lower down : the inner ridge is 

 not easily examined. The two condyles are evident. Examine their relations to one 

 another, and notice that a line drawn between them has the top of the olecranon on 

 or just above it when the arm is straight, but below it when the elbow is bent : it is 

 placed much nearer the inner condyle. It is possible to examine the back of the bone 

 just above the outer condyle, but not so easily on the inner side. 



Ossification. 



The bone is preformed in cartilage. A centre for the shaft appears in the sixth 

 to seventh week, and at birth the ends are cartilaginous, but in about a fifth of the total 

 cases a small centre is present in the articular head at birth. 



The upper is the growing end, and three centres, for the head, greater, and lesser 

 tuberosities, appear in that order between the first and fourth or fifth year, quickly 

 fusing with each other to make the upper epiphysis, so that this is present as a single 

 mass in the fifth or sixth year. It does not unite with the shaft till between the twentieth 

 and twenty-fifth years. 



The lower end has four special centres, three of which are fused to form the lower 

 epiphysis, while the fourth, for the internal condyle, is separated from these by an 

 extension downwards of the shaft : this extension forms the bone between the condyle 

 and trochlea (the part in relation with the ulnar nerve behind) , so that the lower margin 

 of the bone may be said to be made from five centres, of which four are epiphysial. 

 The areas formed by these centres are shown in Fig. 64. 



The centre for the capitulum comes first, in the second to third year, followed by 

 that for the inner condyle in the fifth to eighth year : the trochlear centre appears at 

 about eleven, and the outer condylar nucleus about a year later. Thus these centres 

 for the lower end are all present a few years before puberty. After puberty the exten- 

 sion of the ossification of the shaft takes place, and the three centres of the lower 

 epiphysis fuse with each other and with the shaft about the age of seventeen, followed 

 by junction of the inner condyle with the shaft within a year. 



(See Fig. 68 for the appearance of the cartilaginous lower end and its relation to 

 the capsule.) 



ULNA AND RADIUS. 



These two bones, connected by an interosseous membrane, constitute the skeleton 

 of the forearm. They articulate with the humerus above and carry the hand below. 

 The ulna is the inner bone, and forms the main articulation with the humerus, while 

 the radius, placed on its outer side, can rotate its broadened lower end round the ulna 

 in supination and pronation, and articulates directly with the carpus at the wrist : 

 the iilna is only connected with the carpus by ligaments. 



Thus the hand is carried by the radius and moves with it. 



