260 



THE ARTICULATIONS. 



The Interosseous Membrane is a broad and thin plane of fibrous tissue descending 

 obliquely downward and inward, from the interosseous ridge on the radius to that 



Inferior radio-ulnar 

 articulation. 



'fjk('arpal articulations. 



Carpo-metacarpal 

 articulations. 



FIG. 174. Ligaments of wrist and hand. Anterior view. 



on the ulna. It is deficient above, commencing about an inch beneath the tubercle 

 of the radius ; is broader in the middle than at either extremity ; and presents an 

 oval aperture just above its lower margin for the passage of the anterior inter- 

 osseous vessels to the back of the forearm. This ligament serves to connect the 

 bones and to increase the extent of surface for the attachment of the deep muscles. 

 Between its upper border and the oblique ligament an interval exists through 

 which the posterior interosseous vessels pass. Two or three fibrous bands are 

 occasionally found on the posterior surface of this membrane which descend 

 obliquely from the ulna toward the radius, and which have consequently a direc- 

 tion contrary to that of the other fibres. It is in relation, in front, by its upper 

 three-fourths with the Flexor longus pollicis on the outer side, and with the 

 Flexor profundus digitorum on the inner, lying upon the interval between which 

 are the anterior interosseous vessels and nerve ; by its lower fourth, with the 

 Pronator quadratus ; behind, with the Supinator brevis, Extensor ossis metacarpi 

 pollicis, Extensor brevis pollicis, Extensor longus pollicis, Extensor indicis ; and, 

 near the wrist, with the anterior interosseous artery and posterior interosseous 

 nerve. 



3. INFERIOR RADIO-ULNAR ARTICULATION. 



This is a pivot-joint, formed by the head of the ulna received into the sigmoid 

 cavity at the inner side of the lower end of the radius. The articular surfaces are 

 covered by a thin layer of cartilage, and connected together by the following lig- 

 aments : 



Anterior Radio-ulnar. Posterior Radio-ulnar. 



Interarticular Fibro-cartilage. 



The Anterior Radio-ulnar Ligament (Fig. 174) is a narrow band of fibres 

 extending from the anterior margin of the sigmoid cavity of the radius to the 

 anterior surface of the head of the ulna. 



The Posterior Radio-ulnar Ligament (Fig. 175) extends between similar points 

 on the posterior surface of the articulation. 



The Interarticular Fibro-cartilage (Fig. 177) is triangular in shape, and is 



