154 ARTICULATIONS OF THE UPPER LIMB. 



olecranon process, thus completing the • capsule of the joint be- 

 hind. 



The synovial membrane extends upwards on the humerus so far as 

 to line tlie fossas for the coronoid and olecranon processes, and is loose 

 and vascular in the latter positions. It is also prolonged round the neck 

 of the radius, and lines the annular ligament. 



Movements. — Flexion and extension are the only movements which can take 

 place between the humerus and ulna ; and these are limited by the locking- of 

 the coronoid and olecranon processes in the respective fossas of the humerus 

 which receive them. The jjath of motion is in a nearly vertical plane, with a 

 direction slightly outwards. The mner lip of the trochlea being i^rominent 

 below, forms an exi:)ansion which corresponds to an inward projection of the 

 coronoid part of the ulnar surface, and is only brought into use in hexion ; and 

 the outer lip of the trochlea, being everted at the upper and back iiart. forms a 

 surface which is only in use in complete extension, and which then corresjjonds 

 to a surface on the outer aspect of the olecranon, which comes into contact with 

 no other part of the humerus. In flexion and extension the radius moves by its 

 cup-shaped head upon the capitulum, and on the groove between that process 

 iind the trochlea, by a ridge internal to the cup. It is most comi^letely in contact 

 with the humerus in the position of semi-flexion and semi- pronation. In full 

 extension and suiiination, the anterior margin of the head of the radius is barely 

 in contact v.dth the inferior surface of the capitulum. In full flexion the marghi 

 of the head of the radius rests against the pit above the capitulum, 



THE WRIST-JOINT AND ARTICULATIONS OF THE HAND. 



The RADio-a\EPAL articulation, or wrist-joint, is formed between 

 the radius and triangular fibro-cartilage above, and the scaphoid, 

 semilunar and cuneiform bones below. The superior surface, concave 

 1 )oth transversely and from before backwards, is subdivided by linear ele- 

 vations into three parts corresponding to the three bones below, the 

 innermost part being formed by the fibro-cartilage. The inferior 

 surface, convex in both directions, is prolonged further down upon the 

 carpal bones behind than in front. 



The internal lateral ligament is a rounded cord passing directly 

 downwards from the extremity of the styloid process of the ulna, to the 

 cuneiform bone ; it also sends some hbres to the anterior annular 

 ligament and the pisiform bone. 



The external lateral ligament extends from the styloid process of 

 the radius to a rough surface on the outer side of the scaphoid bone, 

 some of its fibres being prolonged to the trapezium, and also to the 

 anterior annular ligament of the wrist. 



The anterior ligament, broad and membranous, consists partly of 

 fibres which have a nearly transverse direction, partly of others which 

 diverge as they descend from the anterior border of the radius to the 

 scai)hoid, semilunar, and cuneiform bones ; some of them are continued 

 to the OS magnum. 



The posterior ligament extends obliquely downwards and inwards, 

 from the extremity of tlie radius, to the posterior surface of the first 

 row of the carpal bones, especially the cuneiform bone ; its fibres are 

 prolonged some distance on the surface of the carpal bones. 



The synovial membrane is reflected from the radius and the 

 triangular fibro-cartilage, on the suiidunding ligaments, and, after 

 lining these, passes to the margins of tiic opposed surface of the carpal 

 bones. 



