186 



Joints of the Upper Extremity. 



Ligamentum annulare radii 



Tendo m. bicipitis .... 

 (cut through) 



Chorda obliqua - 



Radius - 



Membrana 



interossea 



antibrachii 



Ulna 



Processus 

 T- styloideus 

 ulnae 



Discus articularis 

 Processus styloideus radii 



237. Bones of the 



right forearm, with 



ligaments, 



from the volar surface. 



The joint union between the two 

 bones of the forearm, the articulatio 

 radioulnaris is divisible spatially into 

 two portions; these are the articulatio 

 radioulnaris proximalis (0. T. superior 

 radioulnar articulation) between the circum- 

 ferentia articularis of the capitulum radii 

 and the incisura radian's ulnae (see p. 181) 

 and the articulatio radioulnaris distalis 

 (0. T. inferior radioulnar articulation), 

 between the incisura ulnaris radii and the 

 circumferentia articularis of the capitulum 

 ulnae. The latter joint (see also Figs. 238 

 to 240) is surrounded by a loose capsula 

 articularis. This arises on the radius and 

 ulna from the margin of the cartilaginous 

 surfaces and fuses distalward with the 

 margin of the discus articularis, a trian- 

 gular connective tissue plate, sometimes 

 perforated by a slit or hole ; this disc has 

 a broad attachement to the ulnar margin 

 of the incisura ulnaris radii and is fastened 

 by means of a short fibrous cord to the tip 

 of the processus styloideus ulnae (see also 

 Fig. 240). Tin- blind -sac -like bulging of 

 the joint capsule extending proximalward 

 between the circumferentia articularis of 

 the capitulum ulnae and the incisura ulnaris 

 radii is called the recessus sacciformis (see 

 Fig. 240). The articulationes radioulnares 

 proximalis et distalis, in a mechanical sense, 

 form together one joint. The space 

 between the two bones of the foreann is 

 almost completely filled up by the mem- 

 brana interossea antibrachii (inter osseous 

 membrane). This powerful fibrous sheet is 

 stretched out between the cristae interosseae 

 of the radius and of the ulna, is separated 

 proximalward by a large, distalward by a 

 narrow space from the corresponding joint, 

 and possesses several irregular openings for 

 the passage of vessels and nerves ; the fibre 

 bands run in the main obliquely and ex- 

 tend from the radius distalward toward 

 the ulna. In addition the chorda obliqua 

 (0. T. oblique ligament) (see also Figs. 232 

 and 233) extends as a thin rounded fibrous 

 band from the region of the tuberositas 

 ulnae obliquely downward to the region of 

 the tuberositas radii. 



