IOO 



Anatomy of Skeleton 



frieeu. 



the deep muscles which have crossed them lie on the new outer surface, further out 

 and further forward. The tendon of Supinator longus, which is rather in front of 

 the two radial extensors in the marginal group, runs into the base of the projecting 

 mass, spreading out a little and making a definite secondary mark on the Lone : it 

 is partly crossed here by Ext. ossis met., but not by the tendon of Ext. brevis pollicis. 

 Each of these two surfaces on the lower end contains in its groove a synovial sheath 

 for its twc tendons. 



The posterior surface has an oblique narrow groove for the tendon of Ext. longus 

 pollicis, and a broad shallow groove that has in it the anterior interosseous artery and 

 posterior interosseous nerve, covered by Ext. indicis and Ext. communis tendons. 

 The oblique groove has a prominent outer margin separating it from the postero- 

 external surface and ending below in a bony " pulley," on which the tendon turns 



more outwards as it leaves the radius to pass 

 to the thumb. 



Fig. 8 1 is a diagram of the six surfaces on 

 the lower end of the radius. 



The posterior annular ligament is attached 

 to the bony ridges that separate these grooves 

 and holds the tendons in place. The trian- 

 gular fibre-cartilage has its base attached to 

 the inner and lower margin of the lower end 

 of the radius and thus connects it with the 

 ulna and separates the articular surface of the 

 sigmoid notch from that of the lower or carpal 

 aspect. 



The concave carpal articular surface has 

 a ridge running across it from before back- 

 wards : this divides it into an outer area for 

 the scaphoid and an inner for the semilunar hone. The outer area is triangular and 

 extends on to the inner surface of the styloid process : the inner does not cover the 

 whole surface of the semilunar, for this is partly in contact with the fibro-cartilage, 

 but in adduction of the hand the semilunar moves under the radius. 



The attachments of ligaments, etc., on the lower end are shown in Fig. 80. 

 The female bone is said to exhibit a comparatively greater curve than the male 

 bone : otherwise the sexual differences are merely general. 



The head of the radius can be felt in the hollow below the external condyle, where, 

 covered only by ligamentous and aponeurotic structures, it can be recognised by the 

 finger on rotating the forearm : examine it here, and note its changing relation to the 

 condyle as the elbow is bent. The muscular mass of Anconeus lies between it and the 

 olecranon. The tubercle can be felt in thin arms just below the head when the fore- 

 arm is well pronated. The upper part of the shaft of the bone is not easily followed 

 in a well-developed limb, but the lower half can be palpated indirectly on its outer 

 aspect, back and front. The lower end can be felt through and between the tendons 

 behind, externally, and to some extent in front. Notice the level of the styloid pro- 

 cess, lower than the posterior border and situated behind the tendons going to the 

 base of the thumb. 



Ossification of bones of forearm. 



The bones are laid down in cartilage in which shaft centres appear during the 

 seventh week, that for the radius a few days before the ulnar centre. 



FIG. 81. Scheme to show the six surfaces on 

 the lower end of the radius. These are : 

 i, posterior ; 2, postero-external ; 3, 

 external ; 4, anterior ; 5, internal, 

 articular for ulna ; 6, inferior, articular 

 for carpus. Compare with Fig. 80. 

 Extensor tendons lie on surfaces I, 2, 

 and 3, and also over the radio-ulnar 

 joint (Ext. min. dig.) and ulna (Ext. 

 carpi ulnaris) . 



