298 



HUMAN ANATOMY. 



synovial membrane. It narrows below so as to fold under the projecting head, and 

 is attached, chiefly through fibres from the lower border of the lesser sigmoid cavity, 

 to the inner side of the neck. It is connected above with the capsular ligament 

 of the elbow-joint. That the fibres to the neck limit rotation is easily shown by 

 dividing all bands connecting the bones, excepting the orbicular ligament ; for were 

 it not so, the radius could then be turned continuously, which is not the case. It is 

 doubtful, however, whether these fibres become tense by any movement which can 

 occur in the undissected joint. 



The inferior radio-ulnar joint ^ is, when seen from the front, an L-shaped 

 cavity, the vertical part being between the head of the ulna and the hollow on 

 the radius, and the horizontal limb between the ulna and the triangular cartilage,'' 

 which is attached by its base to the border between the inner and lower ends of 

 the radius in such a manner that its distal surface is in the same plane as the 

 lower end of the radius. The apex of the cartilage is attached by a ligament some 

 three millimetres long to'the groove between the head and the styloid process of the 

 ulna and to the inner surface and anterior edge of the latter. Strong bands, 

 inseparable from the ligaments of the wrist, run along its border to the front and 

 back of the articular surface of the radius. The fibro-cartilage is very flexible 



Front of capsule 



Fig. 312. 



Median nerve 



Radial nerve 



Coronoid process 



Inner side of greater 

 sigmoid cavity 



Ulnar nerve 



Orbicular ligament 



Horizontal section through right elbow-joint from above. The trochlea of humerus has been removed. 



and adapts itself to the surfaces of the lower end of the ulna and of the first row of 

 the carpus. Its inner end, however, is not as broad as the lower end of the ulna. 

 It is in some cases perforated. The membrana sacciformis is the synovial mem- 

 brane of this joint, lining the capsule between the ulna and the triangular cartilage, 

 between the ulna and radius, and extending a little above the level of the top of the 

 apposed articular surfaces of these .bones. The capsule enveloping it is delicate, 

 but strengthened in front and behind by ill-marked bands passing between the 

 bones ; these are sometimes described as distinct ayiterior and posterior ligaments. 

 The connection between the lower ends of the bones is much strengthened by the 

 pronator quadratus. 



The ligaments between the shafts are the interosseous membrane and the 

 oblique ligament. The interosseous membrane^ (Fig. 315), composed of fibres 

 running downward and inward, closes, except above, the opening between the bones. 

 Beginning from one to two centimetres below the tubercle of the radius on the 

 anterior surface of the interosseous ridge, and lower from the sharp edge, it connects 

 the two ridges as far as the lower joint, following the posterior division of the inter- 

 osseous ridge of the radius. The upper fibres are nearly transverse. Some long 

 fibres, particularly on the posterior surface, run from ulna to radius. There are 



* Artie, radioulnaris distalis. ^ Discus articularis. ^ Membrana interossea interbrachii. 



