356 



THE ARTICULATIONS 



tion of the lower end of the radius round an axis which corresponds to the centre 

 of the head of the ulna. When the radius rotates forward, pronation of the fore- 

 arm and hand is the result ; and when backward, supination. It will thus be seen 

 that in pronation and supination of the forearm and hand the radius describes a 

 segment of a cone, the axis of which extends from the centre of the head of the 

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

 ulna is not quite stationary, but is circumducted 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 posi- 

 tion of the head of the ulna takes place principally at the shoulder-joint by a rota- 

 tion 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 prominent head of the 

 ulna and the lower end of the radius, when the forearm is in a state of almost complete prona- 

 tion. 



VII. Radio-carpal or Wrist-joint. 



The Wrist is a condyloid articulation. The parts entering into its formation 



are the lower end of the radius and under surface 

 of the interarticular fibro-cartilage, which form 

 together the receiving cavity, and the scaphoid, 

 semilunar, and cuneiform bones, which form the 

 condyle. The articular surface of the radius and 

 the under surface of the inter-articular fibro-car- 

 tilage 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 sur- 

 faces of the articulation are covered with cartilage, 

 and connected together by a capsule, which is 

 divided into the following ligaments : 



External Lateral. Anterior. 



Internal Lateral. Posterior. 



qnum 



EXTENSOR SEC. 

 INTERN. POLL. 



The External Lateral Ligament (radio-carpal) 

 (Fig. 248) 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 (ulno-carpat) 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 Ligament is a broad membranous 

 band, attached, above, to the anterior margin of 

 the lower end of the radius, its styloid process and 

 the ulna : its fibres pass downward arid inward to 

 be inserted into the palmar surface of the scaphoid, 

 semilunar, and cuneiform bones, some of the fibres 

 being 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 semilunar and cuneiform bones. This ligament is per- 

 1 See Journ. of Anat. and Pkys., vol. xix., parts ii., iii., and iv. 



FIG. 250. Longitudinal section of the 

 right forearm, hand, and third finger, 

 viewed from the ulnar aspect. (After 

 Braune.) 



