Limbs : Upper Limb 97 



The ridge is made by a thin aponeurotic fascia which covers the deep muscles and 

 is continued on to the surface of Supinator brevis above : the origins of the deep 

 muscles are mapped out by their aponeurotic fibres. 



Extensor Carpi Ulnaris. Origin is prolonged from the external condyle and 

 capsule to the subcutaneous border by an aponeurotic sheet which is attached to the 

 line (Fig. 79) below the insertion of Anconeus, and is often described as an " inter- 

 muscular septum " on this aspect of the Anconeus. The origin is from the middle 

 third of the subcutaneous border by aponeurosis, and thus the muscle comes to lie on 

 and play over the smooth area on the extensor surface : the continuation of this 

 surface downwards leads to the groove for the tendon by the styloid process, where 

 there is a synovial sheath. 



Subcutaneous Border. This only extends to the lower fourth of the shaft : below 

 this it cannot be found. The explanation is that it is made by the attachment of the 

 deep fascia, rendered aponeurotic internally by the fusion with the aponeurosis of 

 origin of F. carpi ulnaris, and externally with that of Ext. carpi ulnaris : between 

 these two aponeuroses the ridge is subcutaneous. At the lower end, however, the 

 deep fascia plays over the bone without firm attachment, as this would interfere with 

 the radio-ulnar movements to some extent. 



Fig. 76 shows how the position and shape of the ulna are such as to allow the 

 ulnar nerve to come at once into a plane in front of the bone without turning forward : 

 articulate the arm and forearm and extend the latter, and it can be seen at once that 

 the internal condyle is in front of the plane of the ulna, so that the nerve can run 

 straight down to its position on the anterior annular ligament. At the same time the 

 ulnar artery, in coming inwards and downwards off the Brachialis anticus, must have 

 a backward inclination, and this brings it into relation with the nerve after a very 

 short course. 



The female bone is smaller and lighter, with less marked muscular ridges : the 

 head of the bone is more globular and knob-like in the female than in the male. 



The whole length of the bone can be felt by the finger from the olecranon, along 

 the subcutaneous border, to the styloid process. Observe the relation of the olecranon 

 to the condyles of the humerus (q.v.) when the elbow is straight and bent, and notice 

 that its distance from the inner condyle increases as flexion progresses. .The styloid 

 process is found on the back of the wrist when the forearm is supinated, but, on prona- 

 tion, the rounded mass seen and felt here is the articular head itself, uncovered by the 

 forward and inward movement of the radius, and the styloid process appears now to be 

 on the inner and posterior aspect of the wrist : the apparent change is really due, of 

 course, to the swinging round of the hand with the Radius. 



RADIUS. 



The concave upper surface of the head, covered by cartilage, is in contact with 

 the nearly spherical capitulum of the humerus, and has a double movement on this, 

 gliding during flexion and extension and rotating during pronation and supination. 

 The circumference of the head is also covered by cartilage, and is altogether intra- 

 articular and in synovial contact with the ulna internally and orbicular ligament for 

 the rest of its extent : the synovial membrane comes down for a little distance below 

 the level of the orbicular ligament, to be reflected on to the neck of the bone. 



The tubercle has a rough posterior part into which the tendon of the Biceps is 

 inserted, and a front part somewhat facetted, against which the tendon would play 

 in pronation and flexion, and which is therefore guarded by a bursa that is partly 

 enclosed behind by the tertdon. The oblique ligament runs downwards and outwards 



