314 



THE ARTICULATIONS, OR JOINTS 



of the radius to the middle of the head of the ulna. In this movement, however, the ulna is 

 not quite stationary, but rotates a little in the opposite direction. So that it also describes the 

 segment of a cone, though of smaller size than that described by the radius. The movement which 



causes this alteration in the position of the head of the 

 ulna takes place principally at the shoulder-joint by the 

 rotation of the humerus, but possibly also to a slight 

 extent at the elbow-joint. 1 



Surface Form. The position of the inferior radio- 

 ulnar joint may be ascertained by feeling for a slight 

 groove at the back of the wrist, between the promi- 

 nent head of the ulna and the lower end of the radius, 

 when the forearm is in a state of almost complete pro- 

 nation. 



VII. Radiocarpal or Wrist-joint (Articulatio 

 Radiocarpea) (Figs. 253, 254). 



The wrist is a condyloid articulation. The 

 parts entering into its formation are the lower 

 end of the radius and under surface of the 



articular disk, which form together the receiving 

 cavity, and the scaphoid, semilunar. and the 

 cuneiform bones, which form the condyle. The 

 articular surface of the radius and the under 

 surface of the articular disk are the receiving 

 cavity, forming together a transversely elliptical 

 concave surface. The articular surfaces of 

 the scaphoid, semilunar, and cuneiform bones 

 form together a smooth, convex surface, the 

 condyle, which is received into the concavity 

 above mentioned. All the bony surfaces of the 

 articulation are covered by hyaline cartilage, 

 and are connected by a capsule, which is 

 divided into the following ligaments: 



External Lateral. 

 Internal Lateral. 



Anterior. 

 Posterior. 



FIG. 255. Longitudinal section of the 



right forearm, hand, and middle finger, 



viewed from the ulnar aspect. (After 

 Baurne.) 



The external lateral ligament (ligamentum 

 collateral carpi radiale) (Fig. 253) extends 

 from the summit of the styloid process of the 

 radius to the outer side of the scaphoid, some 

 of its fibres being prolonged to the trapezium 

 and annular ligament. 



The internal lateral ligament (ligamentum cottaterale carpi ulnare) (Fig. 253) 

 is a rounded cord, attached, above, to the extremity of the styloid process of the 

 ulna, and dividing, below, into two fasciculi, which are attached, one to the inner 

 side of the cuneiform bone, the other to the pisiform bone and annular ligament. 

 The anterior or volar ligament (ligamentum radiocarpeum volare] (Fig. 253) 

 is a broad, membranous band, attached, above, to the anterior margin of the 

 lower end of the radius, to its styloid process, and to the ulna ; its fibres pass down- 

 ward and inward to be inserted into the palmar surface of the scaphoid, semilunar, 

 and cuneiform bones. Some of the fibres are continued to the os magnum. In 

 addition to this broad membrane there is a distinct rounded fasciculus, superficial 

 to the rest, which passes from the base of the styloid process of the ulna to the semi- 



1 See Hultkrantz, Das Ellenbogen Gelenk und seine Mechanik, Jena, 1897. 



