THOEACIC LIMBS 



597 



FIG. 455. 



THE SCAPHO-LUNAR. 



General Description. The Scapho-lunar is the largest bone of 

 the carpus, and forms the greater part of its proximal aspect. It lies 

 on the radial side of the hand, and articulates with 

 the lower end of the radius and with all the other 

 carpal bones (Fig. 455). It is in the main rectan- 

 gular in form, but appears irregular, owing largely 

 to the prolongation of the radio-palmar corner into 

 a distinct process. The length of this process is 

 about equal to a third of the radio-ulnar width of 

 the bone, and its direction is to the radial and 

 palmar sides of the wrist. The scapho-lunar pre- 

 sents for examination six surfaces. 



The proximal surface (Fig. 456) may be recog- 

 nized as the largest, smoothest, and most convex. 

 It consists of two parts, the surface of the bone 

 proper and the surface of the process. The former, 

 which is much larger, is almost rectangular, and 

 nearly twice as wide as long. From side to side it 

 is distinctly convex, and from before backward it is 

 convex at the ulnar end and concave at the radial 

 end. It is covered with cartilage, and articulates with the lower end 

 of the radius. Its dorsal border is smooth and rounded and passes 

 without a definite line into the dorsal surface. Its ulnar border is 

 straight or slightly emarginate. The ulnar half of the palmar border 



FTG. 456. 

 Palmar Side. 



Radial Side. / %^ ^ ^ Ulnar Side. 



I J|| 4 With Radius. 



With Sesamoid. 



Dorsal Side. 



LEFT SCAPHO-LUNAR, PROXIMAL SURFACE. 



is rounded, and the radial half is elevated to a sharp crest, which is 

 continued as the proximal surface of the process. The radial border 

 is directed from the front obliquely backward and outward and is 



POSITION OF SCAPHO- 

 LUNAR. 



