ARTICULATIONS OF THE UPPER EXTREMITIES. 291 



extensors, and, as Mr. Boyer observes, seems to be intended 

 rather to afford origin to muscles than to unite the bones. Its 

 superior part is thinner above, and a large opening exists there 

 for the passing of the interosseal vessels to the back of the fore 

 arm. Its inferior part, is thicker, where openings also exist, 

 but small, for the passing of vessels. There are some other 

 smaller perforations in this ligament, but of less note than the 

 preceding, also for vessels. On its posterior face there are one 

 or two bands, the fibres of which decussate the other fibres. 



Beside the interosseal ligament, there is one called round 

 (Teres,) situated obliquely between the two bones at the upper 

 part of the interval which separates them. It arises from the 

 base of the coronoid process, just below the insertion of the 

 brachialis internus; and descending obliquely outwards, is in- 

 serted into the radius below its tubercle. Its object is to bind 

 the bones together, at a point which is weakened by the defi- 

 ciency of the interosseal ligament. This deficiency is, in fact, 

 much larger than the simple passing of the vessels requires; 

 for it is also large enough to allow the tubercle of the radius to 

 rotate freely, a motion which would have been checked by the 

 presence of the ligament. 



Of the Articulations of the Wrist. 



Several articular cavities present themselves at this point. 

 One is between the lower part of the ulna and the radius, ano- 

 ther between the carpal bones and those of the fore arm, and 

 a third between the two rows of carpal bones. One general 

 capsule invests these parts. 



1. The Lower Radio-Ulnar Articulation is surrounded by a 

 section of the fibres belonging to the general capsular ligament 

 of the wrist: their attachment, however, is so loose, that they 

 allow the bones to rotate freely upon each other, besides which 

 they are not so abundant as in other places. When this joint 

 is cut open, it will be seen that the head of the ulna is covered 

 with cartilage, and that the cartilage which covers the carpal 

 articular face of the radius, projects between the ulna and the 

 os cuneiforme; and covers also the sigmoid cavity of the radius; 

 so that a cavity for receiving the convex head of the ulna is 



